scsi: lpfc: Fix RQ buffer leakage when no IOCBs available

The driver is occasionally seeing the following SLI Port error, requiring
reset and reinit:

 Port Status Event: ... error 1=0x52004a01, error 2=0x218

The failure means an RQ timeout. That is, the adapter had received
asynchronous receive frames, ran out of buffer slots to place the frames,
and the driver did not replenish the buffer slots before a timeout
occurred. The driver should not be so slow in replenishing buffers that a
timeout can occur.

When the driver received all the frames of a sequence, it allocates an IOCB
to put the frames in. In a situation where there was no IOCB available for
the frame of a sequence, the RQ buffer corresponding to the first frame of
the sequence was not returned to the FW. Eventually, with enough traffic
encountering the situation, the timeout occurred.

Fix by releasing the buffer back to firmware whenever there is no IOCB for
the first frame.

[mkp: typo]

Link: https://lore.kernel.org/r/20200128002312.16346-2-jsmart2021@gmail.comSigned-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

@@ -17950,6 +17950,10 @@ lpfc_prep_seq(struct lpfc_vport *vport, struct hbq_dmabuf *seq_dmabuf)
 			list_add_tail(&iocbq->list, &first_iocbq->list);
 		}
 	}
+	/* Free the sequence's header buffer */
+	if (!first_iocbq)
+		lpfc_in_buf_free(vport->phba, &seq_dmabuf->dbuf);
+
 	return first_iocbq;
 }