rsx: Fix const RTV/DSV cast from texture cache

rpcs3/Emu/RSX/GL/GLRenderTargets.h

@@ -113,6 +113,11 @@ namespace gl
 	{
 		return ensure(dynamic_cast<gl::render_target*>(t));
 	}
+
+	static inline const gl::render_target* as_rtt(const gl::texture* t)
+	{
+		return ensure(dynamic_cast<const gl::render_target*>(t));
+	}
 }
 
 struct gl_render_target_traits

rpcs3/Emu/RSX/GL/GLTextureCache.h

@@ -393,7 +393,7 @@ namespace gl
 			return managed_texture.get();
 		}
 
-		gl::render_target* get_render_target()
+		gl::render_target* get_render_target() const
 		{
 			return gl::as_rtt(vram_texture);
 		}

rpcs3/Emu/RSX/VK/VKRenderTargets.h

@@ -85,6 +85,11 @@ namespace vk
 		return ensure(dynamic_cast<vk::render_target*>(t));
 	}
 
+	static inline const vk::render_target* as_rtt(const vk::image* t)
+	{
+		return ensure(dynamic_cast<const vk::render_target*>(t));
+	}
+
 	struct surface_cache_traits
 	{
 		using surface_storage_type = std::unique_ptr<vk::render_target>;

rpcs3/Emu/RSX/VK/VKTextureCache.h

@@ -163,7 +163,7 @@ namespace vk
 			return managed_texture;
 		}
 
-		vk::render_target* get_render_target()
+		vk::render_target* get_render_target() const
 		{
 			return vk::as_rtt(vram_texture);
 		}