powerpc: Max next_tb to prevent from replaying timer interrupt

With lazy interrupt, we always call __check_irq_replaysome with
decrementers_next_tb to check if we need to replay timer interrupt.
So in hotplug case we also need to set decrementers_next_tb as MAX
to make sure __check_irq_replay don't replay timer interrupt
when return as we expect, otherwise we'll trap here infinitely.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>