SystemUI: fix MediaProjection cast crash

Clicking on the "cast" icon of an app using the MediaProjection API will
crash as the code assume that it is a device.

java.lang.ClassCastException: android.media.projection.MediaProjectionInfo cannot be cast to android.media.MediaRouter$RouteInfo
	at com.android.systemui.statusbar.policy.CastControllerImpl.startCasting(CastControllerImpl.java:177)
	at com.android.systemui.qs.tiles.CastTile$CastDetailAdapter.onDetailItemClick(CastTile.java:237)
	at com.android.systemui.qs.QSDetailItems$1.onClick(QSDetailItems.java:177)
	at android.view.View.performClick(View.java:4756)
	at android.view.View$PerformClick.run(View.java:19749)
	at android.os.Handler.handleCallback(Handler.java:739)
	at android.os.Handler.dispatchMessage(Handler.java:95)
	at android.os.Looper.loop(Looper.java:135)
	at android.app.ActivityThread.main(ActivityThread.java:5221)
	at java.lang.reflect.Method.invoke(Native Method)
	at java.lang.reflect.Method.invoke(Method.java:372)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

Change-Id: Icfdf745c03da7bd1bbb228e06005f55324c1b8fa