drm/i915/skl: Assume no scaling is available when things are not as expected

Cdclk < crtc_clock is not allowed and suggests a different problem
elsewhere in the code.

It is more robust and safe to assume no scaling is possible in
this case with no other downsides since it will also WARN_ON_ONCE
so that this definitely gets noticed.

Call it an assert to help new platform bring-up in simulation.

v2: Better commit msg and use WARN_ON_ONCE to signify the unexpectedness.

v3: Move zero crtc_clock check under the warn. (Ville)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -13453,7 +13453,7 @@ skl_max_scale(struct intel_crtc *intel_crtc, struct intel_crtc_state *crtc_state
 	crtc_clock = crtc_state->base.adjusted_mode.crtc_clock;
 	cdclk = to_intel_atomic_state(crtc_state->base.state)->cdclk;
 
-	if (!crtc_clock || !cdclk)
+	if (WARN_ON_ONCE(!crtc_clock || cdclk < crtc_clock))
 		return DRM_PLANE_HELPER_NO_SCALING;
 
 	/*