V4L/DVB (3797): Always wait for diseqc queue to become ready before transmitting a diseqc message

The previous DISEQC code didn't wait, so it was unreliable

Signed-off-by: Yeasah Pell <yeasah at schwide.net>
Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>