IB/SA: Use correct free function

Fixes a direct call to kfree_skb when nlmsg_free should be used.

Fixes: 2ca546b9 ('IB/sa: Route SA pathrecord query through netlink')
Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>