drm/i915: Drop the forcewake count inc/dec around register read on VLV

VLV is the only platform where we increment/decrement the forcewake
count around register access. Drop the inc/dec on VLV to make the
forcewake code a bit more unified.

The inc/dec are not necessary since we hold the uncore lock around
the whole operation.

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