clockevents: tick_broadcast_device can become static

The variable tick_broadcast_device is not used outside of the
file where it is defined, so let's make it static.
Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time/tick-broadcast.c

@@ -27,7 +27,7 @@
  * timer stops in C3 state.
  */
 
-struct tick_device tick_broadcast_device;
+static struct tick_device tick_broadcast_device;
 /* FIXME: Use cpumask_var_t. */
 static DECLARE_BITMAP(tick_broadcast_mask, NR_CPUS);
 static DECLARE_BITMAP(tmpmask, NR_CPUS);