iscsi-target: remove unused debug code

Last user of buf was removed with c6037cc5.  While at it,
free_cpumask_var() handles a NULL argument just fine, so remove the
conditionals.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>