Add missing check that device is connected prior to access it.

[   55.358652] BUG: KASAN: null-ptr-deref in rdma_init_qp_attr+0x4a/0x2c0
[   55.359389] Read of size 8 at addr 00000000000000b0 by task qp/618
[   55.360255]
[   55.360432] CPU: 1 PID: 618 Comm: qp Not tainted 4.16.0-rc1-00071-gcaf61b1b #91
[   55.361693] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
[   55.363264] Call Trace:
[   55.363833]  dump_stack+0x5c/0x77
[   55.364215]  kasan_report+0x163/0x380
[   55.364610]  ? rdma_init_qp_attr+0x4a/0x2c0
[   55.365238]  rdma_init_qp_attr+0x4a/0x2c0
[   55.366410]  ucma_init_qp_attr+0x111/0x200
[   55.366846]  ? ucma_notify+0xf0/0xf0
[   55.367405]  ? _get_random_bytes+0xea/0x1b0
[   55.367846]  ? urandom_read+0x2f0/0x2f0
[   55.368436]  ? kmem_cache_alloc_trace+0xd2/0x1e0
[   55.369104]  ? refcount_inc_not_zero+0x9/0x60
[   55.369583]  ? refcount_inc+0x5/0x30
[   55.370155]  ? rdma_create_id+0x215/0x240
[   55.370937]  ? _copy_to_user+0x4f/0x60
[   55.371620]  ? mem_cgroup_commit_charge+0x1f5/0x290
[   55.372127]  ? _copy_from_user+0x5e/0x90
[   55.372720]  ucma_write+0x174/0x1f0
[   55.373090]  ? ucma_close_id+0x40/0x40
[   55.373805]  ? __lru_cache_add+0xa8/0xd0
[   55.374403]  __vfs_write+0xc4/0x350
[   55.374774]  ? kernel_read+0xa0/0xa0
[   55.375173]  ? fsnotify+0x899/0x8f0
[   55.375544]  ? fsnotify_unmount_inodes+0x170/0x170
[   55.376689]  ? __fsnotify_update_child_dentry_flags+0x30/0x30
[   55.377522]  ? handle_mm_fault+0x174/0x320
[   55.378169]  vfs_write+0xf7/0x280
[   55.378864]  SyS_write+0xa1/0x120
[   55.379270]  ? SyS_read+0x120/0x120
[   55.379643]  ? mm_fault_error+0x180/0x180
[   55.380071]  ? task_work_run+0x7d/0xd0
[   55.380910]  ? __task_pid_nr_ns+0x120/0x140
[   55.381366]  ? SyS_read+0x120/0x120
[   55.381739]  do_syscall_64+0xeb/0x250
[   55.382143]  entry_SYSCALL_64_after_hwframe+0x21/0x86
[   55.382841] RIP: 0033:0x7fc2ef803e99
[   55.383227] RSP: 002b:00007fffcc5f3be8 EFLAGS: 00000217 ORIG_RAX: 0000000000000001
[   55.384173] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc2ef803e99
[   55.386145] RDX: 0000000000000057 RSI: 0000000020000080 RDI: 0000000000000003
[   55.388418] RBP: 00007fffcc5f3c00 R08: 0000000000000000 R09: 0000000000000000
[   55.390542] R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000400480
[   55.392916] R13: 00007fffcc5f3cf0 R14: 0000000000000000 R15: 0000000000000000
[   55.521088] Code: e5 4d 1e ff 48 89 df 44 0f b6 b3 b8 01 00 00 e8 65 50 1e ff 4c 8b 2b 49
8d bd b0 00 00 00 e8 56 50 1e ff 41 0f b6 c6 48 c1 e0 04 <49> 03 85 b0 00 00 00 48 8d 78 08
48 89 04 24 e8 3a 4f 1e ff 48
[   55.525980] RIP: rdma_init_qp_attr+0x52/0x2c0 RSP: ffff8801e2c2f9d8
[   55.532648] CR2: 00000000000000b0
[   55.534396] ---[ end trace 70cee64090251c0b ]---

Fixes: 75216638 ("RDMA/cma: Export rdma cm interface to userspace")
Fixes: d541e455

 ("IB/core: Convert ah_attr from OPA to IB when copying to user")
Reported-by:  <syzbot+7b62c837c2516f8f38c8@syzkaller.appspotmail.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>