When using a fixed 1.8V regulator for vqmmc (indicated by vs18_enable),
attempting to change the voltage produces spurious errors since the
regulator cannot be adjusted. The driver currently attempts the voltage
change, receives -ENOSYS from the regulator subsystem, and reports:
Setting to 1.8V error: -38
esdhc_set_voltage error -5
Fix this by checking vs18_enable early in esdhc_set_voltage() and
returning -ENOTSUPP for all voltage switch requests, not just 3.3V.
This prevents unnecessary regulator operations and eliminates the
error messages when the hardware is correctly configured with a fixed
1.8V supply.
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
fd30e492cc