media: ddbridge: stv09xx: detach frontends on lnb failure

While the failure handling in dvb_input_attach() has been improved lately
so any tuner failure won't result in demod driver modules with a
usecount > 0 anymore (thus requiring rmmod -f), there's still an issue
with stv090x and stv0910 based tuner modules, in that LNB driver attach
failures leave an attached demod frontend driver behind which have a
usecount of > 0 in this failure case, due to them not being detached/
released. Fix this by detaching the demod frontends if the LNB driver
fails.

Richard tested and verified the changes with STV0910 hardware, thus adding
his Tested-by.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Tested-by: Richard Scobie <rascobie@slingshot.co.nz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>