iio: sx9310: Enable vdd and svdd regulators at probe

Enable the main power supply (vdd) and digital IO power supply (svdd)
during probe so that the i2c communication and device works properly on
boards that aggressively power gate these supplies.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Daniel Campello <campello@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>