V4L/DVB (6639): xc2028: correct divisor length

The frequency divisor should only be four bytes long.  Also, display the
frequency and divisor correctly in the debug output.

Signed-off-by: Chris Pascoe <c.pascoe@itee.uq.edu.au>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>