drm/qxl: Fix qxl_noop_get_vblank_counter()

This breaks under the vblank timestamp cleanup patch
by Daniel Vetter. Also it is pointless to return anything
but zero (or any other constant) if the function doesn't
actually query a hw vblank counter. The bogus return of
the current drm vblank counter via direct readout or via
drm_vblank_count() is found in many of the new kms drivers,
but it does exactly nothing different from returning any
arbitrary constant - it's a no operation.

Let's simply return 0 - Easy and fast.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/qxl/qxl_drv.c

@@ -198,7 +198,7 @@ static int qxl_pm_restore(struct device *dev)
 
 static u32 qxl_noop_get_vblank_counter(struct drm_device *dev, int crtc)
 {
-	return dev->vblank[crtc].count.counter;
+	return 0;
 }
 
 static int qxl_noop_enable_vblank(struct drm_device *dev, int crtc)