ppc/pnv: Fix LPC POWER8 register sanity check

ppc/pnv: Fix LPC POWER8 register sanity check

POWER8 does not have the ISA IRQ -> SERIRQ routing system of later
CPUs, instead all ISA IRQs are sent to the CPU via a single PSI
interrupt. There is a sanity check in the POWER8 case to ensure the
routing bits have not been set, because that would indicate a
programming error.

Those bits were incorrectly specified because of ppc bit numbering
fun. Coverity detected this as an always-zero expression.

Cc: qemu-stable@nongnu.org
Reported-by: Cédric Le Goater <clg@redhat.com>
Resolves: Coverity CID 1558829 (partially)
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>