drm/arc: Drop crtc check in arc_pgu_update

It's redundant, drm core guarantees that state->fb is set iff
state->crtc is set.

v2: I had a misconception about simple helpers here and thought they
filter this out. They don't. Issue reported by Eugeniy.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210112084358.2771527-10-daniel.vetter@ffwll.ch

drivers/gpu/drm/arc/arcpgu_crtc.c

@@ -135,7 +135,7 @@ static void arc_pgu_update(struct drm_simple_display_pipe *pipe,
 	struct arcpgu_drm_private *arcpgu;
 	struct drm_gem_cma_object *gem;
 
-	if (!pipe->plane.state->crtc || !pipe->plane.state->fb)
+	if (!pipe->plane.state->fb)
 		return;
 
 	arcpgu = pipe_to_arcpgu_priv(pipe);