package/cramfs: Needs zlib

cramfs.mk contains

CRAMFS_DEPENDENCIES = zlib

but this dependency was missing in Config.in.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>