time/jiffies: Make refined_jiffies static

sparse complains:

  CHECK   kernel/time/jiffies.c
kernel/time/jiffies.c:92:20: warning: symbol 'refined_jiffies' was not
			     	      declared. Should it be static?

Its only used in file scope. Make it static.
Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/32342.1552379915@turing-police

kernel/time/jiffies.c

@@ -89,7 +89,7 @@ struct clocksource * __init __weak clocksource_default_clock(void)
 	return &clocksource_jiffies;
 }
 
-struct clocksource refined_jiffies;
+static struct clocksource refined_jiffies;
 
 int register_refined_jiffies(long cycles_per_second)
 {