drm/virtio: Fix a double free in virtio_gpu_cmd_map()

drm/virtio: Fix a double free in virtio_gpu_cmd_map()

This is freed both here and in the caller (virtio_gpu_vram_map()) so
it's a double free.  The correct place is only in the caller.

Fixes: 16845c5d5409 ("drm/virtio: implement blob resources: implement vram object")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20201030114808.GD3251003@mwanda
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>