QSTileLogger: use TileSpec for logbuffer map key

The key used to be of type String, which was inconsistent with the type
of the key in LogModule. This fault resulted in a build failure when
QSTileLogger was being referenced in PolicyModule.

Flag: NONE
Fixes: 310008787
Test: manual. mp droid should not fail when adding a tile that uses
QSTileLogger.
Test: atest QSTileLoggerTest

Change-Id: I546b934309d77e65f56a74dca8a69ae5a392dc49