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/km_compat/lib.rs b/keystore2/src/km_compat/lib.rs
index 56c35bf..8d7310b 100644
--- a/keystore2/src/km_compat/lib.rs
+++ b/keystore2/src/km_compat/lib.rs
@@ -260,7 +260,7 @@
         if let Some(mut extras) = extra_params {
             kps.append(&mut extras);
         }
-        let result = legacy.begin(purpose, &blob, &kps, None);
+        let result = legacy.begin(purpose, blob, &kps, None);
         assert!(result.is_ok(), "{:?}", result);
         result.unwrap()
     }