drm/atomic-helper: Use old/new state in drm_atomic_helper_commit_planes_on_crtc()

Update drm_atomic_helper_commit_planes_on_crtc() to use explicit old/new
states instead of relying on obj->state.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180626204144.14769-1-ville.syrjala@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>