drm: Pass the display mode to drm_calc_vbltimestamp_from_scanoutpos()

Rather than using crtc->hwmode, just pass the relevant mode to
drm_calc_vbltimestamp_from_scanoutpos(). This removes the last hwmode
usage from core drm.

Reviewed-by: mario.kleiner.de@gmail.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 46bf8ae..3f57c77 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1401,7 +1401,8 @@
 						 int crtc, int *max_error,
 						 struct timeval *vblank_time,
 						 unsigned flags,
-						 struct drm_crtc *refcrtc);
+						 const struct drm_crtc *refcrtc,
+						 const struct drm_display_mode *mode);
 extern void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 					    const struct drm_display_mode *mode);