lib: fix sparse warnings

lib: fix sparse warnings

Fixes the following sparse warning messages:

    lib/ovsdb-idl.c:146:12: error: symbol 'table_updates_names' was not
    declared. Should it be static?
    lib/ovsdb-idl.c:147:12: error: symbol 'table_update_names' was not
    declared. Should it be static?
    lib/ovsdb-idl.c:148:12: error: symbol 'row_update_names' was not
    declared. Should it be static?

Reported-by: Joe Stringer <joe@ovn.org>
Signed-off-by: Andy Zhou <azhou@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>