stat: sum sync_stat before reassigning bool first

stat: sum sync_stat before reassigning bool first

Currently, sum_stat(&dst->sync_stat, &src->sync_stat, first, false)
is called after the summing the stats on a per ddir level.

The for-loop that sums the stats on a per ddir level will reassign
bool first to false when unified_rw_rep is used.

This means that the call to sum_stat() for sync_stat will be called
with first == false, even when it is the first sync_stat being summed,
leading to incorrect sync_stat calculations when unified_rw_rep is used.

In order to ensure that sync_stat is not incorrectly affected by the
reassignment of first, move the sync_stat summing before the for-loop.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20211215122557.95600-1-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>