[media] firewire: firedtv-avc: potential buffer overflow

"program_info_length" is user controlled and can go up to 4095.  The
operand[] array has 509 bytes so we need to add a limit here to prevent
buffer overflows.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>