drm/i915/overlay: Use the ioctl parameters directly

The user parameters to put_image are not copied back to userspace
(DRM_IOW), and so we can modify the ioctl parameters (having already been
copied to a temporary kernel struct) directly and use those in place,
avoiding another temporary malloc and lots of manual copying.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180906190144.1272-2-chris@chris-wilson.co.uk