media: dvb-frontends: cxd2880: return 0 instead of 'ret'.

Since 'ret' is known to be 0, just return '0'. This fixes 10 smatch warnings:

cxd2880_tnrdmd_dvbt.c:836 cxd2880_tnrdmd_dvbt_check_demod_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt.c:841 cxd2880_tnrdmd_dvbt_check_demod_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt.c:896 cxd2880_tnrdmd_dvbt_check_ts_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt.c:901 cxd2880_tnrdmd_dvbt_check_ts_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt.c:904 cxd2880_tnrdmd_dvbt_check_ts_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt2.c:1027 cxd2880_tnrdmd_dvbt2_check_demod_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt2.c:1032 cxd2880_tnrdmd_dvbt2_check_demod_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt2.c:1087 cxd2880_tnrdmd_dvbt2_check_ts_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt2.c:1092 cxd2880_tnrdmd_dvbt2_check_ts_lock() warn: missing error code? 'ret'
cxd2880_tnrdmd_dvbt2.c:1095 cxd2880_tnrdmd_dvbt2_check_ts_lock() warn: missing error code? 'ret'

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Yasunari Takiguchi <Yasunari.Takiguchi@sony.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>