drm/nouveau/kms/nv50: fix source-rect-only plane updates

This "optimisation" (which was originally meant to skip updating cursor
settings in the core channel on position-only updates) turned out to be
pointless in the final design of the code before it was merged.

Remove it completely, as it breaks other cases.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org [4.10+]

drivers/gpu/drm/nouveau/nv50_display.c

@@ -912,11 +912,9 @@ nv50_wndw_atomic_check(struct drm_plane *plane, struct drm_plane_state *state)
 		if (memcmp(&armw->point, &asyw->point, sizeof(asyw->point)))
 			asyw->set.point = true;
 
-		if (!varm || asym || armw->state.fb != asyw->state.fb) {
 		ret = nv50_wndw_atomic_check_acquire(wndw, asyw, asyh);
 		if (ret)
 			return ret;
-		}
 	} else
 	if (varm) {
 		nv50_wndw_atomic_check_release(wndw, asyw, harm);