pci: Address Rust 1.51.0 clippy issue (upper_case_acroynms)

warning: name `IORegion` contains a capitalized acronym
   --> pci/src/configuration.rs:320:5
    |
320 |     IORegion = 0x01,
    |     ^^^^^^^^ help: consider making the acronym lowercase, except the initial letter (notice the capitalization): `IoRegion`
    |
    = 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>

pci/src/msix.rs

@@ -6,7 +6,7 @@
 extern crate byteorder;
 extern crate vm_memory;
 
-use crate::{PciCapability, PciCapabilityID};
+use crate::{PciCapability, PciCapabilityId};
 use anyhow::anyhow;
 use byteorder::{ByteOrder, LittleEndian};
 use std::io;
@@ -498,8 +498,8 @@ impl PciCapability for MsixCap {
         self.as_slice()
     }
 
-    fn id(&self) -> PciCapabilityID {
-        PciCapabilityID::MSIX
+    fn id(&self) -> PciCapabilityId {
+        PciCapabilityId::MsiX
     }
 }