Fix key alias string comparison

The code was doing a reference compare, not object value comparison,
resulting in failures in the KeyStore setEntry API.

Test: CtsKeystoreTestCases:android.keystore.cts.AndroidKeyStoreTest
Bug: 197138784
Change-Id: I2c5e47283eed5694951869e9ea3853364ddef9d1
Merged-In: I2c5e47283eed5694951869e9ea3853364ddef9d1