[Media Projection] SystemUI ScreenRecorder - Pass correct UID to service

Before, we were passing the multi-user id, and not the process UID.
Media Projection expects to receive the process UID.

Fixes: 319158459
Test: Manual - adb shell dumpsys media_projection - Then check uid
Flag: NONE
Change-Id: Ib2e9a904cdc0279a2d184c7ca76b26708447f472