crypto: nx - Hold the reference returned by of_find_compatible_node

In nx842_pseries_init(), we should hold the reference returned by
of_find_compatible_node() and use it to call of_node_put to keep
refcount balance.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>