scsi: be2iscsi: Replace spin_unlock_bh with spin_lock

spin_unlock_bh back_lock is used in beiscsi_eh_device_reset instead of
spin_lock.

Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>