staging: unisys: visorchipset: Use correct type for dev_no

visorchipset_bus_info.dev_no is only assigned the value of
controlvm_message_packet.create_bus.dev_count, which is a u32. No
point promoting it to a u64.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Tested-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>