doc: Fix DocBook table column count declaration
doc: Fix DocBook table column count declaration

This was broken in 618c9430a82860c84a3be2711eec2c3b43573b2a.

jmcatamney/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,Postgres-XL/Postgres-XL,lisakowen/gpdb,oberstet/postgres-xl,lisakowen/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,pavanvd/postgres-xl,50wu/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,ashwinstar/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,zeroae/postgres-xl,oberstet/postgres-xl,xinzweb/gpdb,ovr/postgres-xl,ashwinstar/gpdb,xinzweb/gpdb,jmcatamney/gpdb,yazun/postgres-xl,yazun/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb,ovr/postgres-xl,ovr/postgres-xl,lisakowen/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,oberstet/postgres-xl,50wu/gpdb,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,lisakowen/gpdb,yazun/postgres-xl,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,greenplum-db/gpdb,zeroae/postgres-xl,lisakowen/gpdb,lisakowen/gpdb,ovr/postgres-xl,xinzweb/gpdb,adam8157/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,zeroae/postgres-xl,ovr/postgres-xl,jmcatamney/gpdb,Postgres-XL/Postgres-XL,techdragon/Postgres-XL,yazun/postgres-xl,50wu/gpdb,yazun/postgres-xl,techdragon/Postgres-XL,techdragon/Postgres-XL,lisakowen/gpdb,adam8157/gpdb,zeroae/postgres-xl,jmcatamney/gpdb,oberstet/postgres-xl,adam8157/gpdb,techdragon/Postgres-XL,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,jmcatamney/gpdb