drm/i915: fix hsw uncached pte

They've changed it ... for no apparent reason. Meh.

V2: remove unused 'is_hsw' field.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>