regulator: stubs: Make stub regulator_get_voltage() return an error

Returning 0 isn't useful, it's not even meaningful if there is a real
regulator there.

Reported-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
1 file changed