drm/i915/guc: Remove one unnecessary variable

No need for local struct drm_device * since dev_priv is the
correct thing to pass in to NEEDS_WaRsDisableCoarsePowerGating
anyway. Changed the macro definition for the latter to reflect
that as well.

v2: Alignment bikeshed.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466518034-24838-1-git-send-email-tvrtko.ursulin@linux.intel.com