drm/ttm: Fix ttm_bo_move_memcpy() for subclassed struct ttm_resource

drm/ttm: Fix ttm_bo_move_memcpy() for subclassed struct ttm_resource

The code was making a copy of a struct ttm_resource. However,
recently the struct ttm_resources were allowed to be subclassed and
also were allowed to be malloced, hence the driver could end up assuming
the copy we handed it was subclassed and worse, the original could have
been freed at this point.

Fix this by using the original struct ttm_resource before it is
potentially freed in ttm_bo_move_sync_cleanup()

v2: Base on drm-misc-next-fixes rather than drm-tip.

Reported-by: Ben Skeggs <skeggsb@gmail.com>
Reported-by: Dave Airlie <airlied@gmail.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: <stable@vger.kernel.org>
Fixes: 4a1f56f7a7f3 ("drm/ttm: Add a generic TTM memcpy move for page-based iomem")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210831071536.80636-1-thomas.hellstrom@linux.intel.com