Fix warnings in preparation for Rust 1.54.0

This CL fixes several new warnings generated by rustc 1.54.0.

Bug: 194812675
Test: m rust
Change-Id: I104aaf07897db4df89dd1598969dd74221bfdd0b
diff --git a/authfs/src/file.rs b/authfs/src/file.rs
index 44d5000..703eddb 100644
--- a/authfs/src/file.rs
+++ b/authfs/src/file.rs
@@ -20,7 +20,7 @@
 
 fn get_local_binder() -> io::Result<VirtFdService> {
     let service_name = "authfs_fd_server";
-    get_interface(&service_name).map_err(|e| {
+    get_interface(service_name).map_err(|e| {
         io::Error::new(
             io::ErrorKind::AddrNotAvailable,
             format!("Cannot reach authfs_fd_server binder service: {}", e),