scsi: snic: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements, since
it won't get confused when someone else holds the lock. This is also a step
towards possibly removing spin_is_locked().

Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: Karan Tilak Kumar <kartilak@cisco.com>
Cc: Sesidhar Baddela <sebaddel@cisco.com>
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: <linux-scsi@vger.kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>