RDMA/drivers: Remove udata check from special QP

GSI QP can't be created from the user space, hence the udata check is
always false (udata == NULL). Remove that check and simplify the flow.

Link: https://lore.kernel.org/r/20200926102450.2966017-9-leon@kernel.org
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>