ext4: Fix null bh pointer dereference in mballoc

Repoted by Adrian Bunk <bunk@kernel.org>:

The Coverity checker spotted the following NULL dereference:

static int ext4_mb_mark_diskspace_used
{
	...
	if (!bitmap_bh)
		goto out_err;
	...
out_err:
	sb->s_dirt = 1;
	put_bh(bitmap_bh);
	...

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 76e5fed..06d1f52 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3069,7 +3069,7 @@
 
 out_err:
 	sb->s_dirt = 1;
-	put_bh(bitmap_bh);
+	brelse(bitmap_bh);
 	return err;
 }