perf env: 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/util/env.c

@@ -149,7 +149,7 @@ static void perf_env__purge_bpf(struct perf_env *env)
 		node = rb_entry(next, struct bpf_prog_info_node, rb_node);
 		next = rb_next(&node->rb_node);
 		rb_erase(&node->rb_node, root);
-		free(node->info_linear);
+		zfree(&node->info_linear);
 		free(node);
 	}