megasas: read addional PCI I/O bar

Some newer cards have the I/O bar at BAR 0, so we need to check
that, too, if we cannot get an address for BAR 2.
Without this patch the new 'megasas-gen2' emulation in qemu
is not detected.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>