media: dvb-usb-v2: lmedm04: remove unnecessary variable in lme2510_stream_restart()

Remove unnecessary variable _ret_ and refactor the code.

Addresses-Coverity-ID: 1226934

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>