[media] xc4000: cleanup dmesg logging

Remove some printk() calls added during driver development, and demote some
other messages to debug only (to reduce dmesg chatter).

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>