HID: appletb-kbd: fix "appletb_backlight" backlight device reference counting

In the Linux kernel, the following vulnerability has been resolved:

HID: appletb-kbd: fix "appletb_backlight" backlight device reference counting

During appletb_kbd_probe, probe attempts to get the backlight device by name. When this happens backlight_device_get_by_name looks for a device in the backlight class which has name "appletb_backlight" and upon finding a match it increments the reference count for the device and returns it to the caller. However this reference is never released leading to a reference leak.

Fix this by decrementing the backlight device reference count on removal via put_device and on probe failure.