Fix the non-working DND toggle

The pendingIntent of the DND toggle was set to immutable previously
which doesn't allow any modification. This CL fixes this by making it
mutable.

Fixes: 191865710
Test: Search "dnd" and make sure the toggle has effect upon modification
Change-Id: Iade256cee8885cb80ade5ca95cc50065c2a78da2

src/com/android/settings/notification/zen/ZenModeSliceBuilder.java

@@ -150,6 +150,6 @@ public class ZenModeSliceBuilder {
         final Intent intent = new Intent(ACTION_ZEN_MODE_SLICE_CHANGED)
                 .setClass(context, SliceBroadcastReceiver.class);
         return PendingIntent.getBroadcast(context, 0 /* requestCode */, intent,
-                PendingIntent.FLAG_CANCEL_CURRENT | PendingIntent.FLAG_IMMUTABLE);
+                PendingIntent.FLAG_CANCEL_CURRENT | PendingIntent.FLAG_MUTABLE);
     }
 }