scsi: lpfc: Fix crash caused by switch reboot

Driver is causing a crash in __lpfc_sli_release_iocbq_s4() when it
dereferences the els_wq which is NULL.

Validate the pring for the els_wq before dereferencing. Reorg the code to
move the pring assignment closer to where it is actually used.

Link: https://lore.kernel.org/r/20210301171821.3427-18-jsmart2021@gmail.com
Co-developed-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_sli.c

@@ -1403,7 +1403,6 @@ __lpfc_sli_release_iocbq_s4(struct lpfc_hba *phba, struct lpfc_iocbq *iocbq)
 			goto out;
 		}
 
-		pring = phba->sli4_hba.els_wq->pring;
 		if ((iocbq->iocb_flag & LPFC_EXCHANGE_BUSY) &&
 			(sglq->state != SGL_XRI_ABORTED)) {
 			spin_lock_irqsave(&phba->sli4_hba.sgl_list_lock,
@@ -1426,9 +1425,9 @@ __lpfc_sli_release_iocbq_s4(struct lpfc_hba *phba, struct lpfc_iocbq *iocbq)
 				      &phba->sli4_hba.lpfc_els_sgl_list);
 			spin_unlock_irqrestore(
 				&phba->sli4_hba.sgl_list_lock, iflag);
-
+			pring = lpfc_phba_elsring(phba);
 			/* Check if TXQ queue needs to be serviced */
-			if (!list_empty(&pring->txq))
+			if (pring && (!list_empty(&pring->txq)))
 				lpfc_worker_wake_up(phba);
 		}
 	}