drm/i915/vlv: remove wait for previous GFX clk disable request

drm/i915/vlv: remove wait for previous GFX clk disable request

Looks like it was introduced in:

commit 27b71431054b2f5ff874de63a9002b3f8ae7b3da
Author: Imre Deak <imre.deak@intel.com>
Date:   Fri Apr 18 16:35:02 2014 +0300

    drm/i915: vlv: factor out vlv_force_gfx_clock and check for pending force-of

but I'm not sure why.  It has caused problems for us in the past (see
85250ddff7a6 "drm/i915/chv: Remove Wait for a previous gfx force-off"
and d7c3922ce239 "drm/i915: vlv: increase timeout when forcing on the
GFX clock") and doesn't seem to be required, so let's just drop it.

References: https://bugs.freedesktop.org/show_bug.cgi?id=89611
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Darren Hart <dvhart@linux.intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Cc: stable@vger.kernel.org # 0e31b1e03202: drm/i915/chv: Remove Wait ...
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>