scsi: lpfc: fix pci hot plug crash in list_add call

scsi: lpfc: fix pci hot plug crash in list_add call

Orabug: 27631736

During pci hot plug, the kernel crashes in a list_add_call

The lookup by tag function will return null if the IOCB is out of range
or does not have the on txcmplq flag set.

Fix: Check for null return from lookup by tag.

Cc: <stable@vger.kernel.org> # 4.12+
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from commit 401bb4169da655f3e5d28d0b208182e1ab60bf2a)
Signed-off-by: Dick dkennedy <dick.kennedy@broadcom.com>
Signed-off-by: Dan Duval <dan.duval@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>