Otherwise the value from the last probe would be retained that possibly is
freed since (the UDC is removed) and therefore no longer relevant. Reproducible
with the dummy UDC:

  modprobe dummy_hcd
  mount -t gadgetfs gadgetfs /dev/gadget
  umount /dev/gadget
  rmmod dummy_hcd
  mount -t gadgetfs gadgetfs /dev/gadget

BUG: unable to handle kernel paging request at ffffffffa066fd9d
Call Trace:
 [<ffffffff811d0cd2>] ? d_alloc_name+0x22/0x50
 [<ffffffff812b74dc>] ? selinux_d_instantiate+0x1c/0x20
 [<ffffffffa067d687>] gadgetfs_create_file+0x27/0xa0 [gadgetfs]
 [<ffffffffa067da70>] ? setup_req.isra.4+0x80/0x80 [gadgetfs]
 [<ffffffffa067dbac>] gadgetfs_fill_super+0x13c/0x180 [gadgetfs]
 [<ffffffff811bc832>] mount_single+0x92/0xc0
 [<ffffffffa067d0f8>] gadgetfs_mount+0x18/0x20 [gadgetfs]
 [<ffffffff811bc8f9>] mount_fs+0x39/0x1b0
 [<ffffffff8116b220>] ? __alloc_percpu+0x10/0x20
 [<ffffffff811d6da3>] vfs_kern_mount+0x63/0xf0
 [<ffffffff811d93be>] do_mount+0x23e/0xac0
 [<ffffffff811660eb>] ? strndup_user+0x4b/0xf0
 [<ffffffff811d9f63>] SyS_mount+0x83/0xc0
 [<ffffffff81695b69>] system_call_fastpath+0x16/0x1b

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Felipe Balbi <balbi@ti.com>