Fix shader error on mobile when using LIGHT_VERTEX

Author: basicer

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.cpp

@@ -587,7 +587,7 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 		actions.usage_defines["COLOR"] = "#define COLOR_USED\n";
 		actions.usage_defines["INSTANCE_CUSTOM"] = "#define ENABLE_INSTANCE_CUSTOM\n";
 		actions.usage_defines["POSITION"] = "#define OVERRIDE_POSITION\n";
-		actions.usage_defines["LIGHT_VERTEX"] = "#define LIGHT_VERTEX\n";
+		actions.usage_defines["LIGHT_VERTEX"] = "#define LIGHT_VERTEX_USED\n";
 
 		actions.usage_defines["ALPHA_SCISSOR_THRESHOLD"] = "#define ALPHA_SCISSOR_USED\n";
 		actions.usage_defines["ALPHA_HASH_SCALE"] = "#define ALPHA_HASH_USED\n";