gpio/board.txt: point to gpiod_set_value

gpiod_set_value() is preffered interface these days, so add a
pointer. Also fix a missing ).

Signed-off-by: Pavel Machek <pavel@ucw.cz>
[Fixed some grammar and reworded]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/gpio/board.txt

@@ -6,7 +6,7 @@ Note that it only applies to the new descriptor-based interface. For a
 description of the deprecated integer-based GPIO interface please refer to
 gpio-legacy.txt (actually, there is no real mapping possible with the old
 interface; you just fetch an integer from somewhere and request the
-corresponding GPIO.
+corresponding GPIO).
 
 All platforms can enable the GPIO library, but if the platform strictly
 requires GPIO functionality to be present, it needs to select GPIOLIB from its
@@ -162,6 +162,9 @@ The driver controlling "foo.0" will then be able to obtain its GPIOs as follows:
 
 Since the "led" GPIOs are mapped as active-high, this example will switch their
 signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
-as active-low, its actual signal will be 0 after this code. Contrary to the legacy
-integer GPIO interface, the active-low property is handled during mapping and is
-thus transparent to GPIO consumers.
+as active-low, its actual signal will be 0 after this code. Contrary to the
+legacy integer GPIO interface, the active-low property is handled during
+mapping and is thus transparent to GPIO consumers.
+
+A set of functions such as gpiod_set_value() is available to work with
+the new descriptor-oriented interface.