drm/amd/display: Fix dc_create failure handling and 666 color depths

[Why]
It is possible (but very unlikely) that constructing dc fails
before current_state is created.

We support 666 color depth in some scenarios, but this
isn't handled in get_norm_pix_clk. It uses exactly the
same pixel clock as the 888 case.

[How]
Check for non null current_state before destructing.

Add case for 666 color depth to get_norm_pix_clk to
avoid assertion.
Signed-off-by: Julian Parkin <julian.parkin@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -502,8 +502,10 @@ void dc_stream_set_static_screen_events(struct dc *dc,
 
 static void destruct(struct dc *dc)
 {
-	dc_release_state(dc->current_state);
-	dc->current_state = NULL;
+	if (dc->current_state) {
+		dc_release_state(dc->current_state);
+		dc->current_state = NULL;
+	}
 
 	destroy_links(dc);
 

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -1839,6 +1839,7 @@ static int get_norm_pix_clk(const struct dc_crtc_timing *timing)
 		pix_clk /= 2;
 	if (timing->pixel_encoding != PIXEL_ENCODING_YCBCR422) {
 		switch (timing->display_color_depth) {
+		case COLOR_DEPTH_666:
 		case COLOR_DEPTH_888:
 			normalized_pix_clk = pix_clk;
 			break;