Fix the following build error:
In file included from ./db/cell.hh:29:0,
from ./db/expiring_cell.hh:26,
from cql3/attributes.hh:31,
from cql3/cql3.cc:33:
./db/composites/cell_name.hh: At global scope:
./db/composites/cell_name.hh:51:36: error: expected class-name before ‘{’ token
class cell_name : public composite {
^
ninja: build stopped: subcommand failed.
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>