cmd: scsi: Fix null pointer dereference in 'scsi reset'

During 'scsi reset', scsi_bus_reset() is called with udevice pointed
to NULL, which causes exception. As a temporary fix, disable the call
for DM SCSI for now.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/scsi.c

@@ -36,7 +36,9 @@ static int do_scsi(cmd_tbl_t *cmdtp, int flag, int argc, char *const argv[])
 	case 2:
 		if (strncmp(argv[1], "res", 3) == 0) {
 			printf("\nReset SCSI\n");
+#ifndef CONFIG_DM_SCSI
 			scsi_bus_reset(NULL);
+#endif
 			ret = scsi_scan(true);
 			if (ret)
 				return CMD_RET_FAILURE;