media: dvb-frontends/stv0910: fix CNR reporting in read_snr()

The CNR value determined in read_snr() is reported via the wrong variable.
It uses FE_SCALE_DECIBEL, which implies the value to be reported in svalue
instead of uvalue. Fix this accordingly.

Picked up from the upstream dddvb-0.9.33 release.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>