media: radio/si470x: kill urb on error

In the probe() function radio->int_in_urb was not killed if an
error occurred in the probe sequence. It was also missing in
the disconnect.

This caused this syzbot issue:

https://syzkaller.appspot.com/bug?extid=2d4fc2a0c45ad8da7e99



Reported-and-tested-by:  <syzbot+2d4fc2a0c45ad8da7e99@syzkaller.appspotmail.com>

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>