perf tools: Fix PMU format parsing test failure

On POWER, the 'perf format parsing' test always fails.

Looks like it is because memset() is being passed number of longs rather
than number of bytes. It is interesting that the test always passes on
my x86 box.

With this patch, the test passes on POWER and continues to pass on x86.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
Link: http://lkml.kernel.org/r/20130117172814.GA18882@us.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>