drivers/isdn: Add module.h to ISDN files implicitly using it.

So that we don't get build failures once the implicit module.h
presence is terminated.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

drivers/isdn/gigaset/interface.c

@@ -14,6 +14,7 @@
 #include "gigaset.h"
 #include <linux/gigaset_dev.h>
 #include <linux/tty_flip.h>
+#include <linux/module.h>
 
 /*** our ioctls ***/