exfat: improve exfat_find_last_cluster

Since exfat_ent_get support cache buffer head, let's apply it to
exfat_find_last_cluster.

Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Reviewed-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: Chi Zhiling

fs/exfat/fatent.c

@@ -296,6 +296,7 @@ int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
 int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
 		unsigned int *ret_clu)
 {
+	struct buffer_head *bh = NULL;
 	unsigned int clu, next;
 	unsigned int count = 0;
 
@@ -308,10 +309,11 @@ int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
 	do {
 		count++;
 		clu = next;
-		if (exfat_ent_get(sb, clu, &next, NULL))
+		if (exfat_ent_get(sb, clu, &next, &bh))
 			return -EIO;
 	} while (next != EXFAT_EOF_CLUSTER && count <= p_chain->size);
 
+	brelse(bh);
 	if (p_chain->size != count) {
 		exfat_fs_error(sb,
 			"bogus directory size (clus : ondisk(%d) != counted(%d))",