ibmvfc: prevent a potential deadlock

My static checker complains that we need to unlock on this path.  Seems
true.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>