s390: remove unneeded dependency for gen_facilities

The dependency between the object and the source is handled by
scripts/Makefile.host, so only "hostprogs-y += gen_facilities"
is fine.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>