V4L/DVB (13008): gspca - stv06xx-hdcs: Fixup exposure

Initialize image size before it's used to initialize exposure.
Work around lack of exposure set hardware latch with a sequence of
register writes in a single I2C command packet.

Signed-off-by: James Blanford <jhblanford@gmail.com>
Signed-off-by: Erik Andrén <erik.andren@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>