[media] ati_remote: switch to single-byte scancodes

The ati_remote driver currently uses 2-byte scancodes. However, one of
those bytes is actually a checksum and therefore shouldn't be considered
as part of the scancode.

Fix the driver to only use the actual data byte as a scancode and to
check the checksum itself. Update the bundled keymaps accordingly.

Since ati_remote was only migrated to the rc subsystem for 3.2, the
previous scancodes weren't emitted on any stable kernel.

Reported-by: George Spelvin <linux@horizon.com>
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>