x86: Do sanity test on the cache record in mrccache_update()

For the cache record to write in mrccache_update(), we should
perform a sanity test to see if it is a valid one.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/x86/include/asm/mrccache.h

@@ -43,7 +43,7 @@ struct mrc_data_container *mrccache_find_current(struct fmap_entry *entry);
  * @entry:	Position and size of MRC cache in SPI flash
  * @cur:	Record to write
  * @return 0 if updated, -EEXIST if the record is the same as the latest
- * record, other error if SPI write failed
+ * record, -EINVAL if the record is not valid, other error if SPI write failed
  */
 int mrccache_update(struct udevice *sf, struct fmap_entry *entry,
 		    struct mrc_data_container *cur);

arch/x86/lib/mrccache.c

@@ -112,6 +112,9 @@ int mrccache_update(struct udevice *sf, struct fmap_entry *entry,
 	ulong base_addr;
 	int ret;
 
+	if (!is_mrc_cache(cur))
+		return -EINVAL;
+
 	/* Find the last used block */
 	base_addr = (1ULL << 32) - CONFIG_ROM_SIZE + entry->offset;
 	debug("Updating MRC cache data\n");