Fix null pointer dereference in appledisplay driver

[Michael Hanselmann <linux-kernel@hansmi.ch>]

Commit 40b20c257a13c5a526ac540bc5e43d0fdf29792a by Len Brown introduced
a null pointer dereference in the appledisplay driver. This patch fixes
it.

Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>

---
I suggest adding this to 2.6.20.1 because this bug causes the kernel to
panic on boot when the driver is compiled in.

diff -Nrup --exclude-from linux-exclude-from linux-2.6.20.orig/drivers/usb/misc/appledisplay.c linux-2.6.20/drivers/usb/misc/appledisplay.c
--- linux-2.6.20.orig/drivers/usb/misc/appledisplay.c	2007-02-09 22:35:56.000000000 +0100
+++ linux-2.6.20/drivers/usb/misc/appledisplay.c	2007-02-10 01:00:28.000000000 +0100
@@ -281,8 +281,8 @@ static int appledisplay_probe(struct usb
 	/* Register backlight device */
 	snprintf(bl_name, sizeof(bl_name), "appledisplay%d",
 		atomic_inc_return(&count_displays) - 1);
-	pdata->bd = backlight_device_register(bl_name, NULL, NULL,
-						&appledisplay_bl_data);
+	pdata->bd = backlight_device_register(bl_name, NULL,
+		pdata, &appledisplay_bl_data);
 	if (IS_ERR(pdata->bd)) {
 		err("appledisplay: Backlight registration failed");
 		goto error;