openvswitch: fix sparse warning incorrect type

fix incorrect type in argument 1 (different address spaces)

../net/openvswitch/datapath.c:169:17: warning: incorrect type in argument 1 (different address spaces)
../net/openvswitch/datapath.c:169:17:    expected void const *
../net/openvswitch/datapath.c:169:17:    got struct dp_nlsk_pids [noderef] __rcu *upcall_portids

Found at: https://patchwork.kernel.org/project/netdevbpf/patch/20210630095350.817785-1-mark.d.gray@redhat.com/#24285159



Signed-off-by: Mark Gray <mark.d.gray@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>