GC: Fix serveral style and nit issues

Signed-off-by: Chaser Huang <huangkangjing@gmail.com>

Author: chaserhkj

crates/cfsctl/src/main.rs

@@ -408,7 +408,7 @@ where
             root_streams,
             force,
         } => {
-            repo.gc(root_images, root_streams, force)?;
+            repo.gc(&root_images, &root_streams, force)?;
         }
         #[cfg(feature = "http")]
         Command::Fetch { url, name } => {