gigaset: fix build failure

Update the dummy LL interface to the LL interface change
introduced by commit daab433c03c15fd642c71c94eb51bdd3f32602c8.
This fixes the build failure occurring after that commit when
enabling ISDN_DRV_GIGASET but neither ISDN_I4L nor ISDN_CAPI.

Impact: bugfix
Signed-off-by: NTilman Schmidt <tilman@imap.cc>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/dummyll.c

@@ -57,12 +57,20 @@ void gigaset_isdn_stop(struct cardstate *cs)
 {
 }
 
-int gigaset_isdn_register(struct cardstate *cs, const char *isdnid)
+int gigaset_isdn_regdev(struct cardstate *cs, const char *isdnid)
 {
-	pr_info("no ISDN subsystem interface\n");
 	return 1;
 }
 
-void gigaset_isdn_unregister(struct cardstate *cs)
+void gigaset_isdn_unregdev(struct cardstate *cs)
+{
+}
+
+void gigaset_isdn_regdrv(void)
+{
+	pr_info("no ISDN subsystem interface\n");
+}
+
+void gigaset_isdn_unregdrv(void)
 {
 }