Input: fix bug in example code

The input example driver uses BTN_0 in the later stages of the
example, so this changes the interrupt routine to match.

Signed-off-by: Steven Whitehouse <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/input/input-programming.txt

···
 
 static void button_interrupt(int irq, void *dummy, struct pt_regs *fp)
 {
-	input_report_key(button_dev, BTN_1, inb(BUTTON_PORT) & 1);
+	input_report_key(button_dev, BTN_0, inb(BUTTON_PORT) & 1);
 	input_sync(button_dev);
 }