drivers: gpu: drm: gma500: Replaced calls kzalloc & memcpy with kmemdup

Replaced calls kzalloc followed by memcpy with call to kmemdup.
Patch found using coccinelle.

Signed-off-by: Alexandru Gheorghiu <gheorghiuandru@gmail.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>