extres: regulator: Fix regulator_status for already enable regulators

If a regulator hasn't been enable by a driver but is enabled in hardware
(most likely enabled by U-Boot), regulator_status will returns that it
is enabled and so any call to regulator_disable will panic as it wasn't
enabled by one of our drivers.

Sponsored by: Diablotin Systems
Differential Revision: https://reviews.freebsd.org/D30293

(cherry picked from commit f52072b06da761c05dcb636dd1a02dea7214174a)