AVRCP1.5: Correct content resolver query for playlist items.

When changepath is requested by remote to playlist items inside
any playlist, we return only single media item count in response.
This is because of incorrect query for content resolver.
This change properly fetches the playlist media items from content
resolver.

Change-Id: I73e1c9ceec611ef806b6f1b4e2d3c5f20509490e