backend: fix bug that mistakeningly selected wrong render device

src/backends/metal/video.rs

@@ -189,6 +189,10 @@ impl BackendDrmDevice for MetalDrmDevice {
             .unwrap_or(self.backend.state.direct_scanout_enabled.get())
     }
 
+    fn gfx_fast_ram_access(&self) -> bool {
+        self.ctx.get().gfx.fast_ram_access()
+    }
+
     fn create_lease(
         self: Rc<Self>,
         lessee: Rc<dyn BackendDrmLessee>,