arm64: smp: Fix pNMI setup after GICv5 rework

Breno reports that pNMIs are not behaving the way they should since
they were reworked for GICv5. Turns out we feed the IRQ number to
the pNMI helper instead of the IPI number -- not a good idea.

Fix it by providing the correct number (duh).

Fixes: ba1004f8 ("arm64: smp: Support non-SGIs for IPIs")
Reported-by: Breno Leitao <leitao@debian.org>
Suggested-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>