Fix two comments in numeric.c

The comments at the top of numeric_int4_safe() and numeric_int8_safe()
mentioned respectively int4_numeric() and int8_numeric().  The intention
is to refer to numeric_int4() and numeric_int8().

Oversights in 4246a977ba.

Reported-by: jian he <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxFfVt7Jx9_j=juxXyP-6tznN8OcvS9E-QSgp0BrD8KUgA@mail.gmail.com

src/backend/utils/adt/numeric.c

@@ -4359,7 +4359,7 @@ int4_numeric(PG_FUNCTION_ARGS)
 }
 
 /*
- * Internal version of int4_numeric() with support for soft error reporting.
+ * Internal version of numeric_int4() with support for soft error reporting.
  */
 int32
 numeric_int4_safe(Numeric num, Node *escontext)
@@ -4429,7 +4429,7 @@ int8_numeric(PG_FUNCTION_ARGS)
 }
 
 /*
- * Internal version of int8_numeric() with support for soft error reporting.
+ * Internal version of numeric_int8() with support for soft error reporting.
  */
 int64
 numeric_int8_safe(Numeric num, Node *escontext)