drivers/isdn: Add export.h for EXPORT_SYMBOL/THIS_MODULE as required.

In preparation of the module.h usage cleanup, call out the header
that we need to get EXPORT_SYMBOL variants and THIS_MODULE into scope.

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

drivers/isdn/gigaset/ev-layer.c

@@ -13,6 +13,7 @@
  * =====================================================================
  */
 
+#include <linux/export.h>
 #include "gigaset.h"
 
 /* ========================================================== */