x86/PCI: VMD: Set bus resource start to 0

The bus always starts at 0.  Due to alignment and down-casting, this
happened to work before, but looked alarmingly incorrect in kernel logs.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>