clockevents: Add module refcount

We want to be able to remove clockevent modules as well. Add a
refcount so we don't remove a module with an active clock event
device.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130425143436.307435149@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time/tick-common.c

@@ -18,6 +18,7 @@
 #include <linux/percpu.h>
 #include <linux/profile.h>
 #include <linux/sched.h>
+#include <linux/module.h>
 
 #include <asm/irq_regs.h>
 
@@ -257,6 +258,9 @@ void tick_check_new_device(struct clock_event_device *newdev)
 			goto out_bc;
 	}
 
+	if (!try_module_get(newdev->owner))
+		return;
+
 	/*
 	 * Replace the eventually existing device by the new
 	 * device. If the current device is the broadcast device, do