[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.