[media] gspca - sn9c20x: Optimize the code of write sequences

The new functions i2c_w1_buf() and i2c_w2_buf() handle the write loops.

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