x86: fix mpparse/acpi interaction

Sitsofe Wheeler reported boot problems on linux-next.

It looks like the same issue as found by Soeren Sandman in 7575217f656a93,
"x86: initialize all fields of mp_irqs[mp_irq_entries]".

But his fix is also not complete, as dstapic is used before it assigned.

Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Bisected-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>