HID: asus: ROG NKey: Ignore portion of 0x5a report

On an Asus G513QY, of the 5 bytes in a 0x5a report, only the first byte
is a meaningful keycode. The other bytes are zeroed out or hold garbage
from the last packet sent to the keyboard.

This patch fixes up the report descriptor for this event so that the
general hid code will only process 1 byte for keycodes, avoiding
spurious key events and unmapped Asus vendor usagepage code warnings.

Signed-off-by: Josh Kilmer <srjek2@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>