mfd: rn5t618: Unregister restart handler on remove

Remove the restart handler registered in probe on device remove.

Fixes: a370f60a58ec ("mfd: rn5t618: Register restart handler")
Signed-off-by: Stefan Agner <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/rn5t618.c

···
 		pm_power_off = NULL;
 	}
 
+	unregister_restart_handler(&rn5t618_restart_handler);
+
 	return 0;
 }