[keystore2] Fix binder import path

Import from the binder crate root instead of binder::public_api for
compatibility with the new crate structure.

Test: m
Bug: 196056781
Change-Id: Ia9695e5493bda965ca9a42989ec5a284407595ce
diff --git a/keystore2/src/authorization.rs b/keystore2/src/authorization.rs
index 04626bc..516a860 100644
--- a/keystore2/src/authorization.rs
+++ b/keystore2/src/authorization.rs
@@ -265,7 +265,7 @@
         challenge: i64,
         secure_user_id: i64,
         auth_token_max_age_millis: i64,
-    ) -> binder::public_api::Result<AuthorizationTokens> {
+    ) -> binder::Result<AuthorizationTokens> {
         let _wp = wd::watch_millis("IKeystoreAuthorization::getAuthTokensForCredStore", 500);
         map_or_log_err(
             self.get_auth_tokens_for_credstore(