perf tools: Set vmlinux_path__nr_entries to 0 in vmlinux_path__exit

Original vmlinux_path__exit() doesn't revert vmlinux_path__nr_entries to
its original state. After the while loop vmlinux_path__nr_entries
becomes -1 instead of 0.

This makes a problem that, if runs twice, during the second run
vmlinux_path__init() will set vmlinux_path[-1] to strdup("vmlinux"),
corrupts random memory.

This patch reset vmlinux_path__nr_entries to 0 after the while loop.
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexei Starovoitov <ast@plumgrid.com
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: pi3orama@163.com
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1431860222-61636-3-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -1819,6 +1819,7 @@ static void vmlinux_path__exit(void)
 {
 	while (--vmlinux_path__nr_entries >= 0)
 		zfree(&vmlinux_path[vmlinux_path__nr_entries]);
+	vmlinux_path__nr_entries = 0;
 
 	zfree(&vmlinux_path);
 }