comerr: avoid comma operator

Avoid unnecessary use of the comma operator in compile_et's
command-line argument processing.

Change-Id: If9308d211676be471f3534e144c7d90214994699
Reviewed-on: http://gerrit.openafs.org/10491
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>