IB/mlx5: Suppress gcc 7 fall-through complaints

Avoid that gcc 7 reports the following warning when building with W=1:

warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: NBart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/cq.c

@@ -124,11 +124,13 @@ static void handle_good_req(struct ib_wc *wc, struct mlx5_cqe64 *cqe,
 	switch (be32_to_cpu(cqe->sop_drop_qpn) >> 24) {
 	case MLX5_OPCODE_RDMA_WRITE_IMM:
 		wc->wc_flags |= IB_WC_WITH_IMM;
+		/* fall through */
 	case MLX5_OPCODE_RDMA_WRITE:
 		wc->opcode    = IB_WC_RDMA_WRITE;
 		break;
 	case MLX5_OPCODE_SEND_IMM:
 		wc->wc_flags |= IB_WC_WITH_IMM;
+		/* fall through */
 	case MLX5_OPCODE_SEND:
 	case MLX5_OPCODE_SEND_INVAL:
 		wc->opcode    = IB_WC_SEND;

drivers/infiniband/hw/mlx5/qp.c

@@ -4053,6 +4053,7 @@ int mlx5_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
 				*bad_wr = wr;
 				goto out;
 			}
+			/* fall through */
 		case MLX5_IB_QPT_HW_GSI:
 			set_datagram_seg(seg, wr);
 			seg += sizeof(struct mlx5_wqe_datagram_seg);