drm/i915: Tune down "GT register while GT waking disabled" message

We've had this since forever, and's randomly reporting issues and as
such causing piles&piles of CI noise. Mika is working on proper debug
infrastructure for this, and on fixing this properly.

Meanwhile make CI more useful for everyone else.

Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93121
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453233656-12955-1-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/i915_drv.c

@@ -1356,7 +1356,7 @@ static void vlv_check_no_gt_access(struct drm_i915_private *dev_priv)
 	if (!(I915_READ(VLV_GTLC_PW_STATUS) & VLV_GTLC_ALLOWWAKEERR))
 		return;
 
-	DRM_ERROR("GT register access while GT waking disabled\n");
+	DRM_DEBUG_DRIVER("GT register access while GT waking disabled\n");
 	I915_WRITE(VLV_GTLC_PW_STATUS, VLV_GTLC_ALLOWWAKEERR);
 }