RDMA/mlx5: Copy response to the user in one place

Update all the places in create QP flows to copy response
to the user in one place.

Link: https://lore.kernel.org/r/20200427154636.381474-34-leon@kernel.org
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>