V4L/DVB (10532): Correction of Stereo detection/setting and signal strength indication

Thanks to Bob Ross <pigiron@gmx.com>
- correction of stereo detection/setting
- correction of signal strength indicator scaling

Signed-off-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>