hrtimer: export ktime_add_safe

We want to use hrtimers in UBIFS (for write-buffer write-back timer).
We need the 'hrtimer_set_expires_range_ns()', which is an in-line
function which uses 'ktime_add_safe()'.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Ingo Molnar <mingo@elte.hu>

kernel/hrtimer.c

@@ -332,6 +332,8 @@ ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs)
 	return res;
 }
 
+EXPORT_SYMBOL_GPL(ktime_add_safe);
+
 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
 
 static struct debug_obj_descr hrtimer_debug_descr;