Following on from the previous commit, we can also do the same with
with legacy OBIO interrupts in pci_pbmA_map_irq().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Artyom Tarasenko <atar4qemu@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>