MidiService: check UID in getDeviceStatus()

If a MIDI device is marked private then make sure
the status can only be obtained by the owner.

Bug: 203549963
Test: see bug for repro steps
Test: atest CtsMidiTestCases
Test: https://source.android.com/devices/audio/midi_test.html
Change-Id: Ibe92f1ca58c7971855453f1794564e95bfb9380d