regulator: cros-ec: Use common cros_ec_command()

Reduce code duplication by using the common cros_ec_command() function
instead of the locally defined variant.

Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220606201825.763788-2-pmalani@chromium.org