drm/i915: Kill vlv_update_rps_cur_delay()

Polling to make sure the current GPU frequency matches the last
requested frequency should not be necessay, and if there's some
throttling involved, the two might not match anyway.

Since we're still seeing this trigger occasionally, and it just
introduces a rather pointless 10 ms delay, it seems like better
to kill it off.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>