RDMA/mlx5: Remove second user copy in create_user_qp

Combine copy_from_user() from create_user_qp() and general code.

Link: https://lore.kernel.org/r/20200427154636.381474-24-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>