package/cups: fix systemd handling

--{dis,en}able-systemd is unrecognized since bump to version 2.4.0 in
commit 07230bfcbc4b3c760a1d96a2595e3557c5e7278b and
https://github.com/OpenPrinting/cups/commit/796bd7cf235b1f738e54ccdcab150ee97827ec23:

configure: WARNING: unrecognized options: --disable-gtk-doc, --disable-gtk-doc-html, --disable-doc, --disable-docs, --disable-documentation, --with-xmlto, --with-fop, --disable-dependency-tracking, --enable-ipv6, --disable-nls, --disable-systemd, --disable-avahi

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 3ebd3bf15ee1570b68cf8defe951f3574f3cda86)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/cups/cups.mk

@@ -40,10 +40,8 @@ CUPS_DEPENDENCIES = \
 
 ifeq ($(BR2_PACKAGE_SYSTEMD),y)
 CUPS_CONF_OPTS += --with-systemd=/usr/lib/systemd/system \
-	--enable-systemd
+	--with-ondemand=systemd
 CUPS_DEPENDENCIES += systemd
-else
-CUPS_CONF_OPTS += --disable-systemd
 endif
 
 ifeq ($(BR2_PACKAGE_DBUS),y)