[media] dw2102: limit messages to buffer size

Otherwise the i2c transfer functions can read or write beyond the end of
stack or heap buffers.

Signed-off-by: Alyssa Milburn <amilburn@zall.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>