[ARM] 3554/1: ARM: Fix dyntick locking

Patch from Tony Lindgren

This patch fixes some dyntick locking issues on ARM as pointed
out by Russell King.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 2d5896b..bcc19fb 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -342,10 +342,10 @@
 
 #ifdef CONFIG_NO_IDLE_HZ
 	if (!(action->flags & SA_TIMER) && system_timer->dyn_tick != NULL) {
-		write_seqlock(&xtime_lock);
+		spin_lock(&system_timer->dyn_tick->lock);
 		if (system_timer->dyn_tick->state & DYN_TICK_ENABLED)
 			system_timer->dyn_tick->handler(irq, 0, regs);
-		write_sequnlock(&xtime_lock);
+		spin_unlock(&system_timer->dyn_tick->lock);
 	}
 #endif