timers: Use already existing function for forwarding timer base

There is an already existing function for forwarding the timer
base. Forwarding the timer base is implemented directly in
get_next_timer_interrupt() as well.

Remove the code duplication and invoke __forward_timer_base() instead.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-11-anna-maria@linutronix.de