btrfs: run clean_dirty_subvols if we fail to start a trans

If we do merge_reloc_roots() we could insert a few roots onto the dirty
subvol roots list, where we hold a ref on them.  If we fail to start the
transaction we need to run clean_dirty_subvols() in order to cleanup the
refs.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index f42589c..e60450c 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4275,6 +4275,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
 	/* get rid of pinned extents */
 	trans = btrfs_join_transaction(rc->extent_root);
 	if (IS_ERR(trans)) {
+		clean_dirty_subvols(rc);
 		err = PTR_ERR(trans);
 		goto out_free;
 	}
@@ -4701,6 +4702,7 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 
 	trans = btrfs_join_transaction(rc->extent_root);
 	if (IS_ERR(trans)) {
+		clean_dirty_subvols(rc);
 		err = PTR_ERR(trans);
 		goto out_free;
 	}