workqueue: Fix type of cpu in trace event

The trace event "workqueue_queue_work" use unsigned int type for
req_cpu, cpu. This casue confusing cpu number like below log.

$ cat /sys/kernel/debug/tracing/trace
cat-317  [001] ...: workqueue_queue_work: ... req_cpu=8192 cpu=4294967295

So, change unsigned type to signed type in the trace event. After
applying this patch, cpu number will be printed as -1 instead of
4294967295 as folllows.

$ cat /sys/kernel/debug/tracing/trace
cat-1338  [002] ...: workqueue_queue_work: ... req_cpu=8192 cpu=-1

Cc: Baik Song An <bsahn@etri.re.kr>
Cc: Hong Yeon Kim <kimhy@etri.re.kr>
Cc: Taeung Song <taeung@reallinux.co.kr>
Cc: linuxgeek@linuxgeek.io
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>