cpumask: align signatures of UP implementations

Between the generic version, and their uniprocessor optimised
implementations, the return types of cpumask_any_and_distribute() and
cpumask_any_distribute() are not identical.  Change the UP versions to
'unsigned int', to match the generic versions.

Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Signed-off-by: Yury Norov <yury.norov@gmail.com>