perf callchain: Use zfree() to avoid possibly accessing dangling pointers

When freeing a->b it is good practice to set a->b to NULL using
zfree(&a->b) so that when we have a bug where a reference to a freed 'a'
pointer is kept somewhere, we can more quickly cause a segfault if some
code tries to use a->b.

Convert one such case in the callchain code.

Cc: Adrian Hunter <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Namhyung Kim <[email protected]>
Link: https://lore.kernel.org/lkml/ZjmcGobQ8E52EyjJ@x1
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: acmel

tools/perf/util/callchain.c

@@ -606,7 +606,7 @@ fill_node(struct callchain_node *node, struct callchain_cursor *cursor)
 					call->brtype_stat = zalloc(sizeof(*call->brtype_stat));
 					if (!call->brtype_stat) {
 						perror("not enough memory for the code path branch statistics");
-						free(call->brtype_stat);
+						zfree(&call->brtype_stat);
 						return -ENOMEM;
 					}
 				}