block-copy: move progress_set_remaining in block_copy_task_end

block-copy: move progress_set_remaining in block_copy_task_end

Moving this function in task_end ensures to update the progress
anyways, even if there is an error.

It also helps in next patch, allowing task_end to have only
one critical section.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210624072043.180494-4-eesposit@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>