Fix key for QuickQuickSettings composable

The keys need to be a parcelable object. So use the string
representation. Without this, composing QuickQuickSettings will crash.

Test: manual, prototype app.
Bug: 349794543
Flag: com.android.systemui.qs_ui_refactor
Change-Id: Iba0ccb1568cfa1996fdbbd4c485ae8ed46fad2f9