mxssb: Add missing return value check

Add missing return value check for sb_load_binary() call.

Signed-off-by: Marek Vasut <marex@denx.de>

mxssb.c

@@ -536,7 +536,7 @@ int main(void)
 	if (ret)
 		return ret;
 
-	sb_load_binary(uboot_filename, 4);
+	ret = sb_load_binary(uboot_filename, 4);
 	if (ret)
 		return ret;