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>
diff --git a/drivers/isdn/i4l/isdn_tty.c b/drivers/isdn/i4l/isdn_tty.c
index e5546cb..2c26b64 100644
--- a/drivers/isdn/i4l/isdn_tty.c
+++ b/drivers/isdn/i4l/isdn_tty.c
@@ -750,6 +750,7 @@
  * supplementary service (CAPI 2.0 part III)
  */
 #include <linux/isdn/capicmd.h>
+#include <linux/module.h>
 
 int
 isdn_tty_capi_facility(capi_msg *cm) {