media: af9035: Remove duplicate error reporting for dvbsky_usb_generic_rw

All error cases inside the function already report errors via dev_err(),
and dvb_usb_v2_generic_rw also reports all error cases, so there is
no silent code path when an error has occurred.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>