payloads/coreinfo: 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: I17811256b04a17539d3ed77f406892ae77e97515
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76848
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/coreinfo/cbfs_module.c

@@ -31,7 +31,7 @@ struct cbheader {
 	u32 align;
 	u32 offset;
 	u32 architecture;
-	u32 pad[1];
+	u32 pad[];
 } __packed;
 
 struct cbfile {
@@ -40,7 +40,7 @@ struct cbfile {
 	u32 type;
 	u32 checksum;
 	u32 offset;
-	char filename[0];
+	char filename[];
 } __packed;
 
 static int filecount = 0, selected = 0, start_row = 0;