perf stat: Expand metric+unit buffer size

Long metric names combined with units may exceed the metric_bf and
lead to truncation. Double metric_bf in size to avoid this.

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20241106004818.2174593-1-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>