Ignore dead code lint on Register's reg field

Author: tarcieri

crates/intrinsic-test/src/json_parser.rs

@@ -17,6 +17,7 @@ struct ReturnType {
 #[serde(untagged, deny_unknown_fields)]
 pub enum ArgPrep {
     Register {
+        #[allow(dead_code)]
         #[serde(rename = "register")]
         reg: String,
     },