media: si470x: Avoid card name truncation

The "card" string only holds 31 characters (and the terminating NUL).
In order to avoid truncation, use a shorter card description instead of
the current result, "Silicon Labs Si470x FM Radio Re".

Suggested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: 78656acd ("V4L/DVB (7038): USB radio driver for Silicon Labs Si470x FM Radio Receivers")
Fixes: cc35bbdd ("V4L/DVB (12416): radio-si470x: add i2c driver for si470x")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>