tools/accounting/procacct: fix minor errors

The logfile option was documented but not working.  Add it and optimized
the while loop.

Link: https://lkml.kernel.org/r/20241203020550.3145-1-zhangjiao2@cmss.chinamobile.com


Signed-off-by: zhang jiao <zhangjiao2@cmss.chinamobile.com>
Reviewed-by: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>