drm/i915/vlv: reduce GT FIFO error info to a debug message

It indicates a probable BIOS bug, but it appears to be harmless, and
there's nothing the user can do about it anyway, so reduce to a debug
msg.  I've filed a bug with the BIOS folks about it anyway, so hopefully
they'll fix whatever GT SB read they were doing when the GT was off.

References: https://bugs.freedesktop.org/show_bug.cgi?id=69396Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3804,7 +3804,8 @@ static void valleyview_enable_rps(struct drm_device *dev)
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
 	if ((gtfifodbg = I915_READ(GTFIFODBG))) {
-		DRM_ERROR("GT fifo had a previous error %x\n", gtfifodbg);
+		DRM_DEBUG_DRIVER("GT fifo had a previous error %x\n",
+				 gtfifodbg);
 		I915_WRITE(GTFIFODBG, gtfifodbg);
 	}