perf x86 iostat: Use zfree() to reduce chances of use after free

Do defensive programming by using zfree() to initialize freed pointers
to NULL, so that eventual use after free result in a NULL pointer deref
instead of more subtle behaviour.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/util/iostat.c

@@ -10,6 +10,7 @@
 #include <api/fs/fs.h>
 #include <linux/kernel.h>
 #include <linux/err.h>
+#include <linux/zalloc.h>
 #include <limits.h>
 #include <stdio.h>
 #include <string.h>
@@ -100,8 +101,8 @@ static void iio_root_ports_list_free(struct iio_root_ports_list *list)
 
 	if (list) {
 		for (idx = 0; idx < list->nr_entries; idx++)
-			free(list->rps[idx]);
-		free(list->rps);
+			zfree(&list->rps[idx]);
+		zfree(&list->rps);
 		free(list);
 	}
 }
@@ -390,7 +391,7 @@ void iostat_release(struct evlist *evlist)
 	evlist__for_each_entry(evlist, evsel) {
 		if (rp != evsel->priv) {
 			rp = evsel->priv;
-			free(evsel->priv);
+			zfree(&evsel->priv);
 		}
 	}
 }