perf: script: fix missing ',' for fields option

A comma is missed at the end of line.

Signed-off-by: Changbin Du <changbin.du@huawei.com>
Link: https://lore.kernel.org/r/20231017015524.797065-1-changbin.du@huawei.com


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