HID: asus: use spinlock to protect concurrent accesses

asus driver has a worker that may access data concurrently.
Proct the accesses using a spinlock.

Fixes: af22a610 ("HID: asus: support backlight on USB keyboards")
Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>
Link: https://lore.kernel.org/r/20230125-hid-unregister-leds-v4-4-7860c5763c38@diag.uniroma1.it


Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>