btrfs: qgroup: fix initialization of auto inherit array

The "i++" was accidentally left out so it just sets qgids[0] over and
over.

This can lead to unexpected problems, as the groups[1:] would be all 0,
leading to later find_qgroup_rb() unable to find a qgroup and cause
snapshot creation failure.

Fixes: 5343cd93 ("btrfs: qgroup: simple quota auto hierarchy for nested subvolumes")
CC: stable@vger.kernel.org # 6.7+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>