virgl: fix virgl_bo_transfer_{put, get} box struct copy

virgl: fix virgl_bo_transfer_{put, get} box struct copy

Commit 3dfe61ed6ec6 ("gallium: decrease the size of pipe_box - 24 -> 16
bytes") changed the size of pipe_box, but the virgl code was relying on
pipe_box and drm_virtgpu_3d_box structs having the same size/layout doing
a struct copy. Copy the fields one by one instead.

Cc: Marek Olšák <marek.olsak@amd.com>
Cc: Dave Airlie <airlied@redhat.com>
Fixes: 3dfe61ed6ec ("gallium: decrease the size of pipe_box - 24 -> 16 bytes")
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>