Correct SystemMediaRoute2Provider#requestCreateSession

It will call back onSessionCreated or onRequestFailed with
the correct arguments.

Bug: 152932787
Test: manually by cast -> phone multiple times via Output Switcher.
It includes the case that the target route changes (phone -> BT).

Change-Id: Icc324f3e7d6dfde71faa6d3bc919be383e7a5216