zio-user.h: need to include zio.h

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>

include/linux/zio-user.h

@@ -7,6 +7,7 @@
  */
 #ifndef __ZIO_USER_H__
 #define __ZIO_USER_H__
+#include <linux/zio.h>
 
 /*
  * Maximum number of standard and extended attributes. These two values