drm/atomic-helper: remove backoff hack from page_flip

Yay, we can now properly retry in case of deadlocks or whatever!

Also don't forget to remove the transitional crtc->acquire_ctx
assignment again.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170322215058.8671-13-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_plane.c

@@ -875,7 +875,6 @@ retry:
 	ret = drm_modeset_lock(&crtc->cursor->mutex, &ctx);
 	if (ret)
 		goto out;
-	crtc->acquire_ctx = &ctx;
 
 	if (crtc->primary->fb == NULL) {
 		/* The framebuffer is currently unbound, presumably