There's no need to take the write lock when creating sysfs links.

This patch fixes the following BUG:
 BUG: sleeping function called from invalid context at mm/slab.h:416
 in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0
 CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc2-00110-g0b5477d9

 #111
 Backtrace:
 [<0000000040217ac8>] show_stack+0x20/0x38
 [<00000000406fbbb0>] dump_stack+0xb0/0x128
 [<0000000040274090>] ___might_sleep+0x180/0x1b8
 [<0000000040274144>] __might_sleep+0x7c/0xe8
 [<0000000040373874>] kmem_cache_alloc+0x14c/0x1e0
 [<0000000040419514>] __kernfs_new_node+0x84/0x1b8
 [<000000004041b09c>] kernfs_new_node+0x3c/0x78
 [<000000004041e040>] kernfs_create_link+0x40/0xd8
 [<000000004041f320>] sysfs_do_create_link_sd.isra.0+0xb0/0x130
 [<000000004041f3d4>] sysfs_create_link+0x34/0x58
 [<000000004011b4a4>] pdc_stable_init+0x2c4/0x458
 [<0000000040200250>] do_one_initcall+0x70/0x1d8
 [<0000000040101644>] kernel_init_freeable+0x27c/0x390
 [<000000004020be44>] kernel_init+0x24/0x1c0

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Helge Deller <deller@gmx.de>