perf_event: Initialize data.period in perf_swevent_hrtimer()

In current code in perf_swevent_hrtimer(), data.period is not
initialized, The result is obvious wrong:

 # ./perf record -f -e cpu-clock make
 # ./perf report
 # Samples: 1740
 #
 # Overhead   Command                                   ......
 # ........  ........  ..........................................
 #
   1025422183050275328.00%        sh  libc-2.9.90.so ...
   1025422183050275328.00%      perl  libperl.so     ...
   1025422168240043264.00%      perl  [kernel]       ...
   1025422030011210752.00%      perl  [kernel]       ...

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: <stable@kernel.org>
LKML-Reference: <4B14E220.2050107@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -4010,6 +4010,7 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 	event->pmu->read(event);
 
 	data.addr = 0;
+	data.period = event->hw.last_period;
 	regs = get_irq_regs();
 	/*
 	 * In case we exclude kernel IPs or are somehow not in interrupt