Doc bug in example input driver

[Steven Whitehouse <swhiteho@redhat.com>]

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 <swhiteho@redhat.com>

diff --git a/Documentation/input/input-programming.txt b/Documentation/input/input-programming.txt
index 47fc868..81905e8 100644
--- a/Documentation/input/input-programming.txt
+++ b/Documentation/input/input-programming.txt
@@ -22,7 +22,7 @@ static struct input_dev *button_dev;
 
 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);
 }