Fix audio focus evaluation order for display update

Change 1f9196a8 introduced
 an issue when trying to ignore audio focus entries in the
 stack that don't use the music stream, or are for transient
 audio focus gain, for remote control display updates.
The bug was that the audio focus stack traversal was not
 starting from the top, as it should. It was using
 the iterator order, which, in the case of a stack, starts
 with the bottom-most entry.
The fix consists in traversing the stack from the top, i.e.
 from the last element of the vector used to hold the stack
 entries.

Bug 7311023

Change-Id: I0c1900dbf98599a621a420ab55531a3eee838fe5