regulator: core: remove some dead code

Originally queue_delayed_work() used to negative error codes or 0 and 1
on success depending if the work was queued or not.  It caused a lot of
bugs where people treated all non-zero returns as failures so we changed
it to return bool instead in d4283e93 ('workqueue: make queueing
functions return bool').  Now it never returns failure.

Checking for negative values causes a static checker warning since it is
impossible based on the bool type.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mark Brown <broonie@kernel.org>