Add missing newline in notification cmd usage

The help/usage text for the notification cmd is not wrapped
correctly when displaying the 'allow_dnd' parameter.

This was introduced in commit 08d381b8.

Test: manual, run cmd notification and check the wrapping
Change-Id: I9a7af1d9e3de91c9124f21eb66817bb73a3512be

services/core/java/com/android/server/notification/NotificationShellCmd.java

@@ -66,7 +66,7 @@ public class NotificationShellCmd extends ShellCommand {
             + "  disallow_listener COMPONENT [user_id (current user if not specified)]\n"
             + "  allow_assistant COMPONENT [user_id (current user if not specified)]\n"
             + "  remove_assistant COMPONENT [user_id (current user if not specified)]\n"
-            + "  set_dnd [on|none (same as on)|priority|alarms|all|off (same as all)]"
+            + "  set_dnd [on|none (same as on)|priority|alarms|all|off (same as all)]\n"
             + "  allow_dnd PACKAGE [user_id (current user if not specified)]\n"
             + "  disallow_dnd PACKAGE [user_id (current user if not specified)]\n"
             + "  reset_assistant_user_set [user_id (current user if not specified)]\n"