cgroup, netclassid: remove double cond_resched

Commit 018d26fc ("cgroup, netclassid: periodically release file_lock
on classid") added a second cond_resched to write_classid indirectly by
update_classid_task. Remove the one in write_classid.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Dmitry Yakunin <zeil@yandex-team.ru>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>