write() methods must work with fixed sized structures as that is the only
way to know where the udata segment starts. The common udata code now
rejects any write() that has a response buffer shorter than the core's
response.

Thus all the checks of out_len for write methods are redundant and can be
removed.
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>