Fix UsbSerialReder for multi-user

When UsbSerialReader checks for package it needs to request package for
the calling user, because UsbSerialReader runs in system_proccess under
u0 and the calling package may not be installed for that user.

Fixes: 146079090
Test: flash and verify that UsbDevice#getSerial() returns correct string
(used to return null before the fix)

Change-Id: I637673165dd364f4728e587a59897184ea5b5620