[PATCH] Shut up per_cpu_ptr() on UP

Currently per_cpu_ptr() doesn't really do anything with 'cpu' in the UP
case.  This is problematic in the cases where this is the only place the
variable is referenced:

  CC      kernel/workqueue.o
  kernel/workqueue.c: In function `current_is_keventd':
  kernel/workqueue.c:460: warning: unused variable `cpu'

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>