percpu: remove unused chunk_alloc parameter from pcpu_get_pages()

pcpu_get_pages() doesn't use chunk_alloc parameter, remove it.

Fixes: fbbb7f4e

 ("percpu: remove the usage of separate populated bitmap in percpu-vm")
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>