busybox: fix installation of cron and ntpd scripts in the default config

Fixes: 0b24850e97 ("busybox: don't install NTP scripts if NTP isn't configured")
Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/utils/busybox/Makefile

@@ -112,10 +112,10 @@ endef
 define Package/busybox/install
 	$(INSTALL_DIR) $(1)/etc/init.d
 	$(CP) $(PKG_INSTALL_DIR)/* $(1)/
-ifneq ($(CONFIG_BUSYBOX_CONFIG_CROND),)
+ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_CROND),)
 	$(INSTALL_BIN) ./files/cron $(1)/etc/init.d/cron
 endif
-ifneq ($(CONFIG_BUSYBOX_CONFIG_NTPD),)
+ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_NTPD),)
 	$(INSTALL_BIN) ./files/sysntpd $(1)/etc/init.d/sysntpd
 	$(INSTALL_BIN) ./files/ntpd-hotplug $(1)/usr/sbin/ntpd-hotplug
 endif