RDMA/uverbs: Use only attrs for the write() handler signature

All of the old arguments can be derived from the uverbs_attr_bundle
structure, so get rid of the redundant arguments. Most of the prior work
has been removing users of the arguments to allow this to be a simple
patch.

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