libmemif: fix the include for ssize_t

Change-Id: I83830e64fb0fc302474837ebfa4f8cb133b1dccf
Type: fix
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/extras/libmemif/src/libmemif.h b/extras/libmemif/src/libmemif.h
index d1c5b05..12d2f1e 100644
--- a/extras/libmemif/src/libmemif.h
+++ b/extras/libmemif/src/libmemif.h
@@ -30,6 +30,7 @@
 #include <inttypes.h>
 #include <sys/types.h>
 #include <sys/timerfd.h>
+#include <sys/types.h>
 
 /*! Error codes */
 typedef enum