regulator_fixed: Do not disable fixed regulator at probe

[manu]

Summary

If the regulator is unused it will be disabled by the regulator_shutdown sysinit.

Test Plan

Tested on pinebook where the backlight is controlled by a fixed-regulator.
The regulator doesn't have a regulator-boot-on param (I'm gonna upstream this) and so we disable it at probe.
We later enable it but this cause the screen to go black.
Linux doesn't disable regulator at boot (at least for fixed-regulator) so better match this to have the same UX.

[mmel]

sys/dev/extres/regulator/regulator_fixed.c

161

This test doesn't works for regulators with active low enable.
Imho, right (and more readable) way is something like:

if (sc->param->boot_on || sc->param->always_on) {
         rv = GPIO_PIN_SET(pin->dev, pin->pin, sc->param->enable_active_high);

then, enable variable can be deleted completely.