drm/i915/vlv: Remove check for Old Ack during forcewake

Based on the HW team inputs. We can should not wait for the old ack,
Waiting for old ack might fail, when other forcewake came before the
present one is desserted.

for example, if forcewake bit 0 was set and before it could get cleared
forcewake bit 1 got set, HW eventually clear bit 0, when the bit 1
is cleared. i.e, bit 1 is still sent then forcewake bit 0 will still be
set.

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Add comment Ville requested.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>