soc/intel/common/mma: 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: Id19193b960935eeffca8e8db60073321592368fe
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76836
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/common/mma.c

@@ -17,7 +17,7 @@
 
 struct mma_data_container {
 	uint32_t mma_signature; /* "MMAD" */
-	uint8_t mma_data[0]; /* Variable size, platform/run time dependent. */
+	uint8_t mma_data[]; /* Variable size, platform/run time dependent. */
 } __packed;
 
 /*