RDMA/cma: make config_item_type const

Make these structures const as they are either passed to the functions
having the argument as const or stored as a reference in the "ci_type"
const field of a config_item structure.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>