drm/i915: fix color order for BGR formats on IVB

This is already fixed for ILK and SNB in the below commit but somehow
IVB is missed.

commit ab2f9df10dd955f1fc0a8650e377588c98f1c029
	Author: Jesse Barnes <jbarnes@virtuousgeek.org>
	Date:   Mon Feb 27 12:40:10 2012 -0800

	drm/i915: fix color order for BGR formats on SNB

Had the wrong bits and field definitions.

Signed-off-by: Vijay Purushothaman <vijay.a.purushothaman@intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>