hrtimer: Add missing sparse annotation for __run_timer()

Sparse reports a warning at __run_hrtimer()
|warning: context imbalance in __run_hrtimer() - unexpected unlock

Add the missing must_hold() annotation.
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200120224347.51843-1-jbi.octave@gmail.com

kernel/time/hrtimer.c

@@ -1477,7 +1477,7 @@ EXPORT_SYMBOL_GPL(hrtimer_active);
 static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 			  struct hrtimer_clock_base *base,
 			  struct hrtimer *timer, ktime_t *now,
-			  unsigned long flags)
+			  unsigned long flags) __must_hold(&cpu_base->lock)
 {
 	enum hrtimer_restart (*fn)(struct hrtimer *);
 	int restart;