cpumask: update pci_bus_show_cpuaffinity to use new cpumask API

Impact: use new cpumask API to reduce stack usage

Replace the local cpumask_t variable with a pointer to the
const cpumask that needs to be printed.

Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>