media: siano: Use kmemdup instead of duplicating its function

kmemdup has implemented the function that kmalloc() + memcpy().
We prefer to kmemdup rather than code opened implementation.

This issue was detected with the help of coccinelle.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
CC: Tomoki Sekiyama <tomoki.sekiyama@gmail.com>
CC: linux-kernel@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>