RDMA/uverbs: Remove out_len checks that are now done by the core

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: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>