documentation: Format button_dev as a pointer.

The docs on creating an input device driver have an example in which
button_dev is a pointer to an input_dev struct. However, in two code
snippets below, button_dev is used as if it is not a pointer. Make these
occurrences of button_dev reflect that it is a pointer.
Signed-off-by: Nelson Penn <nelsonapenn@protonmail.com>
Link: https://lore.kernel.org/r/20220522194953.12097-1-nelsonapenn@protonmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/input/input-programming.rst

@@ -85,15 +85,15 @@ accepted by this input device. Our example device can only generate EV_KEY
 type events, and from those only BTN_0 event code. Thus we only set these
 two bits. We could have used::
 
-	set_bit(EV_KEY, button_dev.evbit);
-	set_bit(BTN_0, button_dev.keybit);
+	set_bit(EV_KEY, button_dev->evbit);
+	set_bit(BTN_0, button_dev->keybit);
 
 as well, but with more than single bits the first approach tends to be
 shorter.
 
 Then the example driver registers the input device structure by calling::
 
-	input_register_device(&button_dev);
+	input_register_device(button_dev);
 
 This adds the button_dev structure to linked lists of the input driver and
 calls device handler modules _connect functions to tell them a new input