lib: test_objpool: Avoid direct access to hrtimer clockbase

The field timer->base->get_time is a private implementation detail and
should not be accessed outside of the hrtimer core.

Switch to the equivalent helper.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20250821-hrtimer-cleanup-get_time-v2-4-3ae822e5bfbd@linutronix.de

Author: t-8ch

lib/test_objpool.c

@@ -164,7 +164,7 @@ static enum hrtimer_restart ot_hrtimer_handler(struct hrtimer *hrt)
 	/* do bulk-testings for objects pop/push */
 	item->worker(item, 1);
 
-	hrtimer_forward(hrt, hrt->base->get_time(), item->hrtcycle);
+	hrtimer_forward_now(hrt, item->hrtcycle);
 	return HRTIMER_RESTART;
 }