IB/mlx4: Remove set but not used variable 'pd'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/infiniband/hw/mlx4/qp.c: In function '_mlx4_ib_destroy_qp':
drivers/infiniband/hw/mlx4/qp.c:1612:22: warning:
 variable 'pd' set but not used [-Wunused-but-set-variable]

Fixes: e00b64f7 ("RDMA: Cleanup undesired pd->uobject usage")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx4/qp.c

@@ -1609,9 +1609,6 @@ static int _mlx4_ib_destroy_qp(struct ib_qp *qp)
 	if (qp->rwq_ind_tbl) {
 		destroy_qp_rss(dev, mqp);
 	} else {
-		struct mlx4_ib_pd *pd;
-
-		pd = get_pd(mqp);
 		destroy_qp_common(dev, mqp, MLX4_IB_QP_SRC, qp->uobject);
 	}