xfs: remove rbpp check from xfs_rtmodify_summary_int

rbpp is always passed into xfs_rtmodify_summary
and xfs_rtget_summary, so there is no need to
test for it in xfs_rtmodify_summary_int.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>