perf symbols: Fix directory descriptor leaking

When I ran "perf kvm ... top", I encountered the following error output.

  Error: perfcounter syscall returned with -1 (Too many open files)

  Fatal: No CONFIG_PERF_EVENTS=y kernel support configured?

Looking into perf, I found perf opens too many directories at
initialization time, but forgets to close them. Here is the fix.

LKML-Reference: <4C230362.5080704@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>