Add missing <malloc.h> and <string.h> includes.

Change-Id: Ia41756e607663d056e7d2fdd7ecbec7e5841a913
diff --git a/toolbox/ionice.c b/toolbox/ionice.c
index 4a182f2..7abc261 100644
--- a/toolbox/ionice.c
+++ b/toolbox/ionice.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <errno.h>