gpio: board.txt: Fix the gpio name example

As explained in this file:

"GPIOs mappings are defined in the consumer device's node, in a property named
<function>-gpios"

So fix the example to match the convention.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Acked-by: NAlexandre Courbot <acourbot@nvidia.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/gpio/board.txt

@@ -31,7 +31,7 @@ through gpiod_get(). For example:
 			    <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
 			    <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
 
-		power-gpio = <&gpio 1 GPIO_ACTIVE_LOW>;
+		power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
 	};
 
 This property will make GPIOs 15, 16 and 17 available to the driver under the