Fix to allow setting URI without recreating ringtone

This patch splits the behavior of creating the media player
and the uri setter and avoids it from being recreated upon
being retrieved by getRingtone which harms performance
causing a double asset load.

Bug: 240621827
Test: Receive a phone call and verify ringtone works

Change-Id: I91563ddcc94f25911937e9fbb35ff36bbe9d3012