[media] ati_remote: Check the checksum

An input report is 4 bytes long, but there are only 12 bits
of actual payload.  The 4 bytes are:
data[0] = 0x14
data[1] = data[2] + data[3] + 0xd5 (a checksum byte)
data[2] = the raw scancode (plus toggle bit in msbit)
data[3] = channel << 4 (the low 4 bits must be zero)

Ignore reports with a bad checksum.

Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>