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: I2ade8a45e195a1d14535605233868ff7aebc0618