staging/lustre/o2iblnd: Don't use cpus_weight

cpus_weight and for_each_cpu_mask are deprecated, so replace them
with cpumask_weight and for_each_cpu respectively.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>