media: usb/dvb-usb-v2/rtl28xxu.c: clean up code to fix smatch warning

Fixes this smatch warning:

drivers/media/usb/dvb-usb-v2/rtl28xxu.c:1040 rtl2832u_frontend_attach() warn: missing error code 'ret'

It is actually a bogus warning since in this particular case ret isn't
meant to be set. But by reworking the code a bit the code is actually
a lot more understandable and it fixes this warning.

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