[ARM] Fix timer damage from d3d74453c3

Move the xtime write mode seqlock into timer_tick(), so it only
surrounds the call to do_timer().

This avoids a deadlock in update_process_times() ...
hrtimer_get_softirq_time() which tries to get a read mode seqlock
on xtime, thereby preventing booting.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-netx/time.c

@@ -33,12 +33,8 @@
 static irqreturn_t
 netx_timer_interrupt(int irq, void *dev_id)
 {
-	write_seqlock(&xtime_lock);
-
 	timer_tick();
 
-	write_sequnlock(&xtime_lock);
-
 	/* acknowledge interrupt */
 	writel(COUNTER_BIT(0), NETX_GPIO_IRQ);