drm/i915: Use the correct GMCH_CTRL register for Sandybridge+
drm/i915: Use the correct GMCH_CTRL register for Sandybridge+

From Chris Wilson
2259bb7720c52941c1d62e078bf019aa88d6f525 in ubuntu 3.8
a885b3ccc74d8e38074e1c43a47c354c5ea0b01e in mainline linux

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars