V4L/DVB (4322): Fix dvb-pll autoprobing

Trent Piepho pointed out that the pll test i2c transmission is slightly
wrong; it was transmitting a zero length message, and then reading from the
PLL. This was wrong; it should only be transmitting a single read i2c message.

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