scsi: qla2xxx: Fix potential NULL pointer dereference

Klocwork tool reported 'cur_dsd' may be dereferenced.  Add fix to validate
pointer before dereferencing the pointer.

Cc: stable@vger.kernel.org
Signed-off-by: Bikash Hazarika <bhazarika@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Link: https://lore.kernel.org/r/20230607113843.37185-3-njavali@marvell.comReviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qla2xxx/qla_iocb.c

@@ -607,7 +607,8 @@ qla24xx_build_scsi_type_6_iocbs(srb_t *sp, struct cmd_type_6 *cmd_pkt,
 	put_unaligned_le32(COMMAND_TYPE_6, &cmd_pkt->entry_type);
 
 	/* No data transfer */
-	if (!scsi_bufflen(cmd) || cmd->sc_data_direction == DMA_NONE) {
+	if (!scsi_bufflen(cmd) || cmd->sc_data_direction == DMA_NONE ||
+	    tot_dsds == 0) {
 		cmd_pkt->byte_count = cpu_to_le32(0);
 		return 0;
 	}