leds: qnap-mcu: Fix state numbering for USB LED

leds: qnap-mcu: Fix state numbering for USB LED

The "@Cx" commands span a number of different functions, from the status
and USB LEDs to the buzzer and power button.

So change the USB-LED enum to start at 0 and adapt the offset accordingly
to not suggest @CD would relate to the USB-LED - while in fact "@CD" is a
state of the status LED.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250804114949.3127417-2-heiko@sntech.de
Signed-off-by: Lee Jones <lee@kernel.org>