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: I3076313ea51c6f4e74029ad9fb45d6f0b6dea460
diff --git a/keystore2/src/keystore2_main.rs b/keystore2/src/keystore2_main.rs
index cf2ba04..f1f01c6 100644
--- a/keystore2/src/keystore2_main.rs
+++ b/keystore2/src/keystore2_main.rs
@@ -63,7 +63,7 @@
         let db_path = Path::new(&dir);
         *keystore2::globals::DB_PATH.write().expect("Could not lock DB_PATH.") =
             db_path.to_path_buf();
-        IdRotationState::new(&db_path)
+        IdRotationState::new(db_path)
     } else {
         panic!("Must specify a database directory.");
     };