Fix SSR not working properly in stereo

servers/rendering/renderer_rd/shaders/effects/specular_merge.glsl

@@ -30,7 +30,7 @@ void main() {
 	vec2 base_arr[3] = vec2[](vec2(-1.0, -1.0), vec2(-1.0, 3.0), vec2(3.0, -1.0));
 	gl_Position = vec4(base_arr[gl_VertexIndex], 0.0, 1.0);
 	uv_interp.xy = clamp(gl_Position.xy, vec2(0.0, 0.0), vec2(1.0, 1.0)) * 2.0; // saturate(x) * 2.0
-#ifdef MULTIVIEW
+#ifdef USE_MULTIVIEW
 	uv_interp.z = ViewIndex;
 #endif
 }