vm-virtio, virtio-devices: Address Rust 1.51.0 clippy issue (upper_case_acronyms)

error: name `TYPE_UNKNOWN` contains a capitalized acronym
  --> vm-virtio/src/lib.rs:48:5
   |
48 |     TYPE_UNKNOWN = 0xFF,
   |     ^^^^^^^^^^^^ help: consider making the acronym lowercase, except the initial letter: `Type_Unknown`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#upper_case_acronyms

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

virtio-devices/src/transport/pci_device.rs

@@ -384,11 +384,11 @@ impl VirtioPciDevice {
         // to firmware without requiring excessive identity mapping.
         let mut use_64bit_bar = true;
         let (class, subclass) = match VirtioDeviceType::from(locked_device.device_type()) {
-            VirtioDeviceType::TYPE_NET => (
+            VirtioDeviceType::Net => (
                 PciClassCode::NetworkController,
                 &PciNetworkControllerSubclass::EthernetController as &dyn PciSubclass,
             ),
-            VirtioDeviceType::TYPE_BLOCK => {
+            VirtioDeviceType::Block => {
                 use_64bit_bar = false;
                 (
                     PciClassCode::MassStorage,