xfs: include reservations in quota reporting

Report all quota usage including the currently pending reservations.  This
avoids the need to flush delalloc space before gathering quota information,
and matches quota enforcement, which already takes the reservations into
account.

This fixes xfstests 270.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>