scsi: lpfc: Check queue pointer before use

The queue pointer might not be valid. The rest of the code checks the
pointer before accessing it. lpfc_sli4_process_missed_mbox_completions is
the only place where the check is missing.

Fixes: 657add4e ("scsi: lpfc: Fix poor use of hardware queues if fewer irq vectors")
Cc: James Smart <jsmart2021@gmail.com>
Link: https://lore.kernel.org/r/20191018162111.8798-1-dwagner@suse.de


Signed-off-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>