s390x/flic: fix compilation of kvm flic

2c21ee76 ("migration: extend VMStateInfo") missed a void -> int
return conversion for kvm_flic_save().

Fixes: 2c21ee76 ("migration: extend VMStateInfo")
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>