Adjust the presentation of two byte scan codes.

The previous implementation worked strictly due to a bug which would
luckily generate roughly the right scan codes, although we would send
more codes than required.

For example, the old implementation would send 0xdf48e0 for 'up key down'
and '0xdfc8e0' for 'up key up'.  The prepended 0xdf is incorrect; the
correct values should be 0x48e0 and 0xc8e0.  Essentially, it stored
the bytes in reverse order and had a bug while flipping them.

This code stores them in the order we transmit them which simplifies
the code.

Signed-off-by: Jeremy White <jwhite@codeweavers.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>