regulator: Add export.h for THIS_MODULE to dummy.c

So that THIS_MODULE is still in scope once we clean up the presence
of module.h being everywhere.

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

drivers/regulator/dummy.c

@@ -16,6 +16,7 @@
  */
 
 #include <linux/err.h>
+#include <linux/export.h>
 #include <linux/platform_device.h>
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>