timers/itimer: 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-v2-2-3ae822e5bfbd@linutronix.de

Author: t-8ch

kernel/time/itimer.c

@@ -163,8 +163,7 @@ void posixtimer_rearm_itimer(struct task_struct *tsk)
 	struct hrtimer *tmr = &tsk->signal->real_timer;
 
 	if (!hrtimer_is_queued(tmr) && tsk->signal->it_real_incr != 0) {
-		hrtimer_forward(tmr, tmr->base->get_time(),
-				tsk->signal->it_real_incr);
+		hrtimer_forward_now(tmr, tsk->signal->it_real_incr);
 		hrtimer_restart(tmr);
 	}
 }