perf stat: Fix CVS output format for non-supported counters

perf stat: Fix CVS output format for non-supported counters

When printing stats in CSV mode, 'perf stat' appends extra separators
when a counter is not supported:

<not supported>,,L1-dcache-store-misses,mesos/bd442f34-2b4a-47df-b966-9b281f9f56fc,0,100.00,,,,

Which causes a failure when parsing fields. The numbers of separators
should be the same for each line, no matter if the counter is or not
supported.

Signed-off-by: Ilya Pronin <ipronin@twitter.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/20180306064353.31930-1-xiyou.wangcong@gmail.com
Fixes: 92a61f6412d3 ("perf stat: Implement CSV metrics output")
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>