SELinux: return EOPNOTSUPP not ENOTSUPP

ENOTSUPP is not a valid error code in the kernel (it is defined in some
NFS internal error codes and has been improperly used other places).  In
the !CONFIG_SECURITY_SELINUX case though it is possible that we could
return this from selinux_audit_rule_init().  This patch just returns the
userspace valid EOPNOTSUPP.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>