util: Use C99 flexible arrays

Use C99 flexible arrays instead of older style of one-element or
zero-length arrays.
It allows the compiler to generate errors when the flexible array does
not occur at the end in the structure.

Change-Id: I6b87680ec9f501945ae266ae4e4927efd2399d56
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76815
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/intelvbttool/intelvbttool.c

@@ -157,7 +157,7 @@ struct bdb_general_definitions {
 	 * number = (block_size - sizeof(bdb_general_definitions))/
 	 *           sizeof(child_device_config);
 	 */
-	struct common_child_dev_config devices[0];
+	struct common_child_dev_config devices[];
 } __attribute__ ((packed));
 
 struct bdb_driver_features {