drm: Check the right variable when setting formats

When setting the video bus supported formats for a display device using
drm_display_info_set_bus_formats(), check for the proper variable after
duplicating memory.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>