[media] af9035: fix broken I2C and USB I/O

There was three small buffer len calculation bugs which caused
driver non-working. These are coming from recent commit:
commit 7760e148
[media] af9035: Don't use dynamic static allocation

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: stable@vger.kernel.org