[media] firewire: use dev_dbg() instead of printk()

A structure for firedtv (struct firedtv) has a member for a pointer to
struct device. In this case, we can use dev_dbg() for debug printing.
This is more preferrable behaviour in device driver development.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>