media: dvb_dummy_fe: change printk to pr_warn

Replaces printk with pr_err to fix warnings from checkpatch.pl

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>