btrfs: fix root leak if its reloc root is unexpected in merge_reloc_roots()

btrfs: fix root leak if its reloc root is unexpected in merge_reloc_roots()

If we have an unexpected reloc_root for our root, we jump to the out label
but never drop the reference we obtained for root, resulting in a leak.
Add a missing btrfs_put_root() call.

Fixes: 24213fa46c70 ("btrfs: do proper error handling in merge_reloc_roots")
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>