drm: store_vblank() is never called with NULL timestamp

Remove the NULL 't_vblank' checks from store_vblank() since that will
never happen.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_irq.c

@@ -83,13 +83,11 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
 
 	assert_spin_locked(&dev->vblank_time_lock);
 
-	if (t_vblank) {
 	/* All writers hold the spinlock, but readers are serialized by
 	 * the latching of vblank->count below.
 	 */
 	tslot = vblank->count + vblank_count_inc;
 	vblanktimestamp(dev, pipe, tslot) = *t_vblank;
-	}
 
 	/*
 	 * vblank timestamp updates are protected on the write side with