workqueue: Fix wq->cpu_pwq leak in alloc_and_link_pwqs() WQ_UNBOUND path

For WQ_UNBOUND workqueues, alloc_and_link_pwqs() allocates wq->cpu_pwq
via alloc_percpu() and then calls apply_workqueue_attrs_locked(). On
failure it returns the error directly, bypassing the enomem: label
which holds the only free_percpu(wq->cpu_pwq) in this function.

The caller's error path kfree()s wq without touching wq->cpu_pwq,
leaking one percpu pointer table (nr_cpu_ids * sizeof(void *) bytes) per
failed call.

If kmemleak is enabled, we can see:

  unreferenced object (percpu) 0xc0fffa5b121048 (size 8):
    comm "insmod", pid 776, jiffies 4294682844
    backtrace (crc 0):
      pcpu_alloc_noprof+0x665/0xac0
      __alloc_workqueue+0x33f/0xa20
      alloc_workqueue_noprof+0x60/0x100

Route the error through the existing enomem: cleanup and any error
before this one.

Cc: stable@kernel.org
Fixes: 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>