[media] soc_camera: use kmemdup()

Instead of calling kzalloc and then copying, use kmemdup(). That
avoids zeroing the data structure before copying.

Found by coccinelle.

Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>