cpumask: use for_each_online_cpu() in drivers/infiniband/hw/ehca/ehca_irq.c

Impact: cleanup

In future, accessing cpu numbers beyond nr_cpu_ids (the runtime limit)
will be undefined.  We can avoid future problems by using
for_each_online_cpu() here.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Tested-by: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Cc: Christoph Raisch <raisch@de.ibm.com>