drm/i915/hdmi: Unify "4:2:0 also" logic between .mode_valid() and .compute_config()

Currently .mode_valid() and .compute_config() have their "4:2:0 also"
logic inverted. Unify things so that we use the same logic on both
sides.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015133921.4609-5-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_hdmi.c

@@ -2179,12 +2179,13 @@ static int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
 
 	ret = intel_hdmi_compute_clock(encoder, crtc_state);
 	if (ret) {
-		if (!intel_hdmi_is_ycbcr420(crtc_state) &&
-		    connector->ycbcr_420_allowed &&
-		    drm_mode_is_420_also(&connector->display_info, adjusted_mode)) {
-			crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
-			ret = intel_hdmi_compute_clock(encoder, crtc_state);
-		}
+		if (intel_hdmi_is_ycbcr420(crtc_state) ||
+		    !connector->ycbcr_420_allowed ||
+		    !drm_mode_is_420_also(&connector->display_info, adjusted_mode))
+			return ret;
+
+		crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
+		ret = intel_hdmi_compute_clock(encoder, crtc_state);
 	}
 
 	return ret;