staging: unisys: visorbus: fix error handling in create_bus_instance

The function get_vbus_header_info returns errors that were being handled
incorrectly. Fix the error handling in create_bus_instance.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>