ext4: fix memory leak in ext4_free_branches

Commit 40389687 moved a call to ext4_forget() out of
ext4_free_branches and let ext4_free_blocks() handle calling
bforget().  But that change unfortunately did not replace the call to
ext4_forget() with brelse(), which was needed to drop the in-use count
of the indirect block's buffer head, which lead to a memory leak when
deleting files that used indirect blocks.  Fix this.

Thanks to Hugh Dickins for pointing this out.

Cc: stable@kernel.org
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -4378,6 +4378,7 @@ static void ext4_free_branches(handle_t *handle, struct inode *inode,
 					(__le32 *) bh->b_data,
 					(__le32 *) bh->b_data + addr_per_block,
 					depth);
+			brelse(bh);
 
 			/*
 			 * Everything below this this pointer has been