ola: needs host-bison and host-flex

Fixes:
http://autobuild.buildroot.net/results/385/385f05b5e1b023b6c4ca220aab897e400b5aeccb/


and a future failure (host-bison).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>