btrfs: fix referenced/exclusive check in squota_check_parent_usage()

btrfs: fix referenced/exclusive check in squota_check_parent_usage()

We compared rfer_cmpr against excl_cmpr_sum instead of rfer_cmpr_sum
which is confusing.

I expect that
rfer_cmpr == excl_cmpr in squota, but it is much better to be consistent
in case of any surprises or bugs.

Reported-by: Chris Mason <clm@meta.com>
Link: https://lore.kernel.org/linux-btrfs/cover.1764796022.git.boris@bur.io/T/#mccb231643ffd290b44a010d4419474d280be5537
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>