regulator: Fix return value of _set_load() stub

regulator: Fix return value of _set_load() stub

The stub implementation of _set_load() returns a mode value which is
within the bounds of valid return codes for success (the documentation
just says that failures are negative error codes) but not sensible or
what the actual implementation does.  Fix it to just return 0.

Reported-by: Cheng-Yi Chiang <cychiang@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>