V4L/DVB (5428): M920x: Detect zero-length I2C messages and fix a typo

Change a 00 to just 0
Detect zero-length I2C messages and return not supported.  I think I know
how to send one, but the problem is getting the slave's ack.  The only
point of a zero-length message is for probing; too see if the slave will
ack its address.  Since we don't know how to get the ack, we can't
support zero-length messages in a useful way, so it's probably best to
just return not supported for them.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>