[media] media: ir-sony-decoder: 15bit function decode fix

The raw Sony IR decoder decodes 15bit messages slightly incorrectly.
To decode the function number, it shifts the bits right by 7 so that the
function is in bits 7:1, masks with 0xFD (0b11111101), and does an 8 bit
reverse so it ends up in bits 6:0. The mask should be 0xFE to correspond
with bits 7:1 (0b11111110).

The old mask had the effect of dropping the MSB of the function number
from bit 6, and leaving the LSB of the device number in bit 7.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>