osd/PrimaryLogPG: clear pin_stats_invalid bit properly on scrub-repair completion

osd/PrimaryLogPG: clear pin_stats_invalid bit properly on scrub-repair completion

We have done audit of stats and the numbers should be all ok by then.
Actually the pin_stats_invalid bit is never set true, so forgetting
to clear pin_stats_invalid here generally does harm. Also we could simply
kill the pin_stats_invalid bit instead but let's not bother with that
complexity either.

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>