Fix confusion of userId vs. uid

There function was trying to get the UserHandle of a userId,
but was instead treating the userId as a uid, and thereby
getting the wrong UserHandle.

Bug: 162543841
Test: com.android.frameworks.telephonytests (i.e. FrameworksTelephonyTests)

Change-Id: I2b6f9c92f1d101fe18a5fdf54b85aa5acf9c94b0