libpayload/drivers/cbmem_console: 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: I3fd3f068ff731e1d9fed7c38ba6815e1eed86450
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76849
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>

payloads/libpayload/drivers/cbmem_console.c

@@ -32,7 +32,7 @@
 struct cbmem_console {
 	uint32_t size;
 	uint32_t cursor;
-	uint8_t body[0];
+	uint8_t body[];
 } __packed;
 
 #define CURSOR_MASK ((1 << 28) - 1)