drm/i915/vlv: For i915_cur_delayinfo, the max frequency reporting wrong value.

The max frequency reporting is not correct.  But there is already an existing
valleyview_rps_max_freq and valleyview_rps_min_freq to get the
frequency.  Use that for i915_cur_delayinfo.

Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>