xfs: strengthen rtalloc query range checks

Strengthen the rtalloc range query checks to make sure that the keys do
not run off the end of the realtime device inappropriately.  Note that
the query range functions require units of rt extents, not blocks,
despite the type name.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>