V4L/DVB (10346): gspca - zc3xx: Fix bad variable type with i2c read.

The returned value of i2c read is a 16 bits word. It was stored in
a 8 bits variable, preventing a sensor to be detected.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>