RDMA/hns: Remove the duplicate calls to ib_copy_validate_udata_in()

RDMA/hns: Remove the duplicate calls to ib_copy_validate_udata_in()

A udata should be read only once per ioctl, not multiple times.
Multiple reads make it unclear what the content is since userspace can
change it between the reads.

Lift the ib_copy_validate_udata_in() out of
alloc_srq_buf()/alloc_srq_db() and into hns_roce_create_srq().

Found by AI.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>