wayland/dma-buf: Fix building without native backend

The usefullnes of Wayland without the native backend is questionable,
but since it's theoretically possible, make it at least compile again.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2202>

src/wayland/meta-wayland-dma-buf.c

@@ -98,7 +98,9 @@ meta_wayland_dma_buf_realize_texture (MetaWaylandBuffer  *buffer,
   EGLImageKHR egl_image;
   CoglEglImageFlags flags;
   CoglTexture2D *texture;
+#ifdef HAVE_NATIVE_BACKEND
   MetaDrmFormatBuf format_buf;
+#endif
 
   if (buffer->dma_buf.texture)
     return TRUE;
@@ -158,11 +160,13 @@ meta_wayland_dma_buf_realize_texture (MetaWaylandBuffer  *buffer,
       return FALSE;
     }
 
+#ifdef HAVE_NATIVE_BACKEND
   meta_topic (META_DEBUG_WAYLAND,
               "[dma-buf] wl_buffer@%u DRM format %s -> CoglPixelFormat %s",
               wl_resource_get_id (meta_wayland_buffer_get_resource (buffer)),
               meta_drm_format_to_string (&format_buf, dma_buf->drm_format),
               cogl_pixel_format_to_string (cogl_format));
+#endif
 
   for (n_planes = 0; n_planes < META_WAYLAND_DMA_BUF_MAX_FDS; n_planes++)
     {