RDMA/uverbs: Mark ioctl responses with UVERBS_ATTR_F_VALID_OUTPUT

When the ioctl interface for the write commands was introduced it did
not mark the core response with UVERBS_ATTR_F_VALID_OUTPUT. This causes
rdma-core in userspace to not mark the buffers as written for valgrind.

Along the same lines it turns out we have always missed marking the driver
data. Fixing both of these makes valgrind work properly with rdma-core and
ioctl.

Fixes: 4785860e ("RDMA/uverbs: Implement an ioctl that can call write and write_ex handlers")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>