drm: Suppress user controlled spam for invalid drm_wait_vblank_ioctl

The ioctl arguments are under control of the user and as such we should
resist any temptation to flood the kernel logs with their errors.
Relegate the DRM_ERROR to a DRM_DEBUG so the user has to opt into
hearing of their own mistakes. (One day we will have a small ringbuffer
attached to the task, so that the concerned process can inspect its own
debug info for EINVAL without them being hitting syslog at all.)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180904115719.24525-1-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_vblank.c

@@ -1541,7 +1541,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
 	if (vblwait->request.type &
 	    ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
 	      _DRM_VBLANK_HIGH_CRTC_MASK)) {
-		DRM_ERROR("Unsupported type value 0x%x, supported mask 0x%x\n",
+		DRM_DEBUG("Unsupported type value 0x%x, supported mask 0x%x\n",
 			  vblwait->request.type,
 			  (_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK |
 			   _DRM_VBLANK_HIGH_CRTC_MASK));