media: dvb-frontends/af9033.c: fix missing error codes

Fixes two smatch warnings:

drivers/media/dvb-frontends/af9033.c:128 af9033_init() warn: missing error code 'ret'
drivers/media/dvb-frontends/af9033.c:855 af9033_read_snr() warn: missing error code 'ret'

Set error codes correctly.

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