scsi: libfc: Fix passing zero to 'PTR_ERR' warning

drivers/scsi/libfc/fc_disc.c:304
 fc_disc_error() warn: passing zero to 'PTR_ERR'

fp may be NULL in fc_disc_error(), use PTR_ERR_OR_ZERO to handle this.

Link: https://lore.kernel.org/r/20200909135432.36772-1-yuehaibing@huawei.comSigned-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libfc/fc_disc.c

@@ -301,8 +301,8 @@ static void fc_disc_error(struct fc_disc *disc, struct fc_frame *fp)
 	struct fc_lport *lport = fc_disc_lport(disc);
 	unsigned long delay = 0;
 
-	FC_DISC_DBG(disc, "Error %ld, retries %d/%d\n",
-		    PTR_ERR(fp), disc->retry_count,
+	FC_DISC_DBG(disc, "Error %d, retries %d/%d\n",
+		    PTR_ERR_OR_ZERO(fp), disc->retry_count,
 		    FC_DISC_RETRY_LIMIT);
 
 	if (!fp || PTR_ERR(fp) == -FC_EX_TIMEOUT) {