extres: regulator: Fix regulator_status for already enable regulators

[manu]

Summary

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.

[mmel]

IMHO, this is wrong change. regulator_status() must report physical state of regulator - if given deice is powered or not. the mmc power sequencer should use similar technique as backlight. But seems like this kind of usage is common - so we can expand regulator framework with uncounted function -> something like regulator_on()/regulator_off()