btrfs: handle errors while updating refcounts in update_ref_for_cow

Since commit fb235dc0 (btrfs: qgroup: Move half of the qgroup
accounting time out of commit trans) the assumption that
btrfs_add_delayed_{data,tree}_ref can only return 0 or -ENOMEM has
been false.  The qgroup operations call into btrfs_search_slot
and friends and can now return the full spectrum of error codes.

Fortunately, the fix here is easy since update_ref_for_cow failing
is already handled so we just need to bail early with the error
code.

Fixes: fb235dc0 (btrfs: qgroup: Move half of the qgroup accounting ...)
Cc: <stable@vger.kernel.org> # v4.11+
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: Edmund Nadolski <enadolski@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>