RDMA/mlx5: Fix remote gid value in query QP

Remote gid is not copied to the right address. Fix it by using
rdma_ah_set_dgid_raw to copy the remote gid value from the QP context on
query QP.

Fixes: 70bd7fb8

 ("RDMA/mlx5: Remove manually crafted QP context the query call")
Link: https://lore.kernel.org/r/20200618112507.3453496-3-leon@kernel.org
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>