[media] radio-si470x-common.c: remove unnecessary kernel log spam

There is no need to report an error in the log, you are already returning
that error to userspace after all.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>