mysql: host-mysql depends on host-zlib

Fixes:

 http://autobuild.buildroot.org/results/ffe/ffe8229f869a67e84c1eacec0055cce8b1906441/



[Thomas: add autobuilder reference.]

Signed-off-by: Marcelo Gutiérrez <kuyurix@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>