cxgb3: Fix warning about using rcu_dereference when not in a rcu-locked section

It is about using rcu_dereference() when not in a rcu-locked section. It only
happens on initialization hence fix the initialization to not rcu_dereference()

Signed-off-by: Jay Fenlason <fenlason@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>