x86/IRQ: ACKTYPE_NONE cannot make it into irq_guest_eoi_timer_fn()

x86/IRQ: ACKTYPE_NONE cannot make it into irq_guest_eoi_timer_fn()

action->ack_type is set once before the timer even gets initialized, and
is never changed later. The timer gets activated only for EOI and UNMASK
types. Hence there's no need to have a respective if() in there. Replace
it by an ASSERT().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>