vm-device: reevaluate #[allow] attributes

Drop stale #[allow]s whose lints no longer fire and convert the
still-needed ones to #[expect] so they warn if the lints stop firing.

Part of #8326.

Signed-off-by: Tushar Khatri <hello@tusharkhatri.in>

vm-device/src/lib.rs

@@ -34,7 +34,7 @@ pub enum PciBarType {
 }
 
 /// Enumeration for device resources.
-#[allow(missing_docs)]
+#[expect(missing_docs)]
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub enum Resource {
     /// IO Port address range.