crypto: iaa - Use cpumask_weight() when rebalancing

If some cpus are offlined, or if the node mask is smaller than
expected, the 'nonexistent cpu' warning in rebalance_wq_table() may be
erroneously triggered.

Use cpumask_weight() to make sure we only iterate over the exact
number of cpus in the mask.

Also use num_possible_cpus() instead of num_online_cpus() to make sure
all slots in the wq table are initialized.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>