regulator: gpio: correct default type

The driver defaults to voltage, not current, type so correct
this in the device tree binding documentation.
Signed-off-by: Hans Holmberg <hans@pixelmunchies.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/gpio-regulator.txt

@@ -13,7 +13,7 @@ Optional properties:
 - startup-delay-us	: Startup time in microseconds.
 - enable-active-high	: Polarity of GPIO is active high (default is low).
 - regulator-type	: Specifies what is being regulated, must be either
-			  "voltage" or "current", defaults to current.
+			  "voltage" or "current", defaults to voltage.
 
 Any property defined as part of the core regulator binding defined in
 regulator.txt can also be used.