HID: wacom_sys: Demote kernel-doc abuse

Fixes the following W=1 kernel build warning(s):

 drivers/hid/wacom_sys.c:1505: warning: Function parameter or member 'wacom' not described in 'wacom_led_next'
 drivers/hid/wacom_sys.c:1505: warning: Function parameter or member 'cur' not described in 'wacom_led_next'

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>