iw_cxgb4: Fix potential NULL dereference in c4iw_fill_res_cm_id_entry()

In the Linux kernel, the following vulnerability has been resolved:

iw_cxgb4: Fix potential NULL dereference in c4iw_fill_res_cm_id_entry()

This condition needs to match the previous "if (epcp->state == LISTEN) {" exactly to avoid a NULL dereference of either "listen_ep" or "ep". The problem is that "epcp" has been re-assigned so just testing "if (epcp->state == LISTEN) {" a second time is not sufficient.