V4L/DVB (11791): xc5000: do not sleep after digital tuning

Don't sleep for 400ms polling the tuner's lock if in digital mode (since the
xc5000 lock status registers appear to only be reliable in analog mode)

Signed-off-by: Devin Heitmueller <devin.heitmueller@gmail.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>