Correct variable names for parsing structured fields (#1531)

Author: apasel422

index.bs

@@ -5408,8 +5408,8 @@ To <dfn noexport>get [=OS registrations=] from a header value</dfn> given a
 [=header value=] |header|:
 
 1. Let |values| be the result of [=structured header/parsing structured fields=]
-    with <var ignore>input_string</var> set to |header| and
-    <var ignore>header_type</var> set to "`list`".
+    with <var ignore>input_bytes</var> set to |header| and
+    <var ignore>field_type</var> set to "`list`".
 1. If parsing failed, return an error.
 1. Let |registrations| be a new [=list=].
 1. [=list/iterate|For each=] |value| of |values|: