video: remove redundant .to_string() in log::debug

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

staging/vhost-device-video/src/video_backends/v4l2_decoder.rs

@@ -346,7 +346,7 @@ impl VideoBackend for V4L2Decoder {
             if format.to_virtio() == 0 {
                 debug!(
                     "Unsupported format for virtio-video ({}), skipping.",
-                    format.to_string()
+                    format
                 );
                 index += 1;
                 continue;