bash: add missing dependency on host-bison

Fixes:
http://autobuild.buildroot.org/results/dfedb4377a95e36e590c9a5a5853e3ed0ecbc247/build-end.log



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>