[media] go7007: fix broken test

The wrong flags field was tested for the GO7007_BOARD_HAS_AUDIO flag: that
flag is in board->main_info.flags, not in board->flags.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>