[media] dvb-bt8xx: convert printks to pr_err()

This module does some printks with the loglevel missing.

pr_err() takes care of adding the KERN_ERR tag and the module name.
So we can simplify the code and add the missing printk loglevel by
using it.

Also add a #define pr_fmt() to make this work, and remove a few
unnecessary periods at the end of messages and bump the loglevel of
"Unknown bttv card type" from KERN_WARNING to KERN_ERR while at it.

Inspired-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>