c/compositor: change idle clear color to black

OLED hmds dont appreciate being driven to white for long periods

Signed-off-by: Carl Philipp Klemm <carl@uvos.xyz>
Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2601>

src/xrt/compositor/shaders/clear.comp

@@ -33,7 +33,7 @@ void main()
 		return;
 	}
 
-	vec4 colour = vec4(from_linear_to_srgb(vec3(0.1)), 1.0);
+	vec4 colour = vec4(0, 0, 0, 1.0);
 
 	imageStore(target, ivec2(offset.x + ix, offset.y + iy), colour);
 }

src/xrt/compositor/util/comp_render_gfx.c

@@ -113,7 +113,7 @@ struct gfx_mesh_data
  */
 
 static const VkClearColorValue background_color_idle = {
-    .float32 = {0.1f, 0.1f, 0.1f, 1.0f},
+    .float32 = {0.0f, 0.0f, 0.0f, 1.0f},
 };
 
 static const VkClearColorValue background_color_active = {