Some wacom w9013 devices have a vddl supply for "low valtage"
requirements. Add support in this driver to turn on this low voltage
supply. We can also drop a handful of error messages because the
regulator core is already printing an error when bulk regulators fail to
enable or disable.

Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Dmitry Torokhov <dtor@chromium.org>
Cc: Doug Anderson <dianders@chromium.org>
Acked-by: NRob Herring <robh@kernel.org>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: NStephen Boyd <swboyd@chromium.org>
Acked-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>