Btrfs: make sure reserve_metadata_bytes doesn't leak out strange errors

The btrfs transaction code will return any errors that come from
reserve_metadata_bytes.  We need to make sure we don't return funny
things like 1 or EAGAIN.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 06a5ee2..4d08ed7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3474,6 +3474,8 @@
 	if (ret < 0)
 		goto out;
 
+	ret = 0;
+
 	/*
 	 * So if we were overcommitted it's possible that somebody else flushed
 	 * out enough space and we simply didn't have enough space to reclaim,
@@ -3496,10 +3498,13 @@
 		goto out;
 
 	ret = -EAGAIN;
-	if (trans || committed)
+	if (trans)
 		goto out;
 
 	ret = -ENOSPC;
+	if (committed)
+		goto out;
+
 	trans = btrfs_join_transaction(root);
 	if (IS_ERR(trans))
 		goto out;