regulator: core: Prevent integer underflow

By using a ratio of delay to poll_enabled_time that is not integer
time_remaining underflows and does not exit the loop as expected.
As delay could be derived from DT and poll_enabled_time is defined
in the driver this can easily happen.

Use a signed iterator to make sure that the loop exits once
the remaining time is negative.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Link: https://lore.kernel.org/r/20220909125954.577669-1-patrick.rudolph@9elements.com


Signed-off-by: Mark Brown <broonie@kernel.org>