IB/mlx4: 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: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx4/cq.c

@@ -768,11 +768,13 @@ repoll:
 		switch (cqe->owner_sr_opcode & MLX4_CQE_OPCODE_MASK) {
 		case MLX4_OPCODE_RDMA_WRITE_IMM:
 			wc->wc_flags |= IB_WC_WITH_IMM;
+			/* fall through */
 		case MLX4_OPCODE_RDMA_WRITE:
 			wc->opcode    = IB_WC_RDMA_WRITE;
 			break;
 		case MLX4_OPCODE_SEND_IMM:
 			wc->wc_flags |= IB_WC_WITH_IMM;
+			/* fall through */
 		case MLX4_OPCODE_SEND:
 		case MLX4_OPCODE_SEND_INVAL:
 			wc->opcode    = IB_WC_SEND;