fio: syslet.h build fix

update syslet.h to build fine even if __user is not defined.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/syslet.h b/syslet.h
index 85f0ebc..d89abd4 100644
--- a/syslet.h
+++ b/syslet.h
@@ -10,6 +10,10 @@
  * User-space API/ABI definitions:
  */
 
+#ifndef __user
+# define __user
+#endif
+
 /*
  * This is the 'Syslet Atom' - the basic unit of execution
  * within the syslet framework. A syslet always represents