staging: unisys: removed unused 'visor_device.respond_to_device_create'

The respond_to_device_create flag was used previously when we used to
delay responses to create requests until the drivers were finished
loading. This behaviour was removed some time ago, yet the field still
existed, while never being referenced or even initialized.

Signed-off-by: Alexander Curtin <alexander.curtin@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>