RDMA/hns: Uninitialized variable in modify_qp_init_to_rtr()

The "dmac" variable is used before it is initialized.

Fixes: 494c3b31 ("RDMA/hns: Refactor the QP context filling process related to WQE buffer configure")
Link: https://lore.kernel.org/r/20200529083918.GA1298465@mwanda


Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>