Update src/util/std_code.h

Co-Authored-By: Peter Schrammel <peterschrammel@users.noreply.github.com>

Author: thomasspriggs

src/util/std_code.h

@@ -635,7 +635,7 @@ inline code_assertt &to_code_assert(codet &code)
 /// has a value which corresponds to the value of a given expression
 /// (or expressions).
 /// When working with the C front end, calls to the `__CPROVER_input` intrinsic
-/// can be added to the input code in order add instances of this class to the
+/// can be added to the input code in order add instructions of this type to the
 /// goto program.
 /// The first argument is expected to be a C string denoting the input
 /// identifier. The second argument is the expression for the input value.