xfsprogs: xfs_quota: return real-time used data as intended

xfsprogs: xfs_quota: return real-time used data as intended

In projects_free_space_data() the real-time used space consumption
is never set.  Instead, that value is returned in the field that
should hold the quota limit.

Found by inspection.  Never seen/noticed because we currently don't
support quotas when a filesystem has a realtime volume.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>