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/selinux/src/lib.rs b/keystore2/selinux/src/lib.rs
index 5197cf6..cf6dfd3 100644
--- a/keystore2/selinux/src/lib.rs
+++ b/keystore2/selinux/src/lib.rs
@@ -130,7 +130,7 @@
     fn deref(&self) -> &Self::Target {
         match self {
             Self::Raw(p) => unsafe { CStr::from_ptr(*p) },
-            Self::CString(cstr) => &cstr,
+            Self::CString(cstr) => cstr,
         }
     }
 }