fast-import: make comments more precise

The former is somewhat imprecise. The latter became out of sync with the
behavior in e814c39c2f (fast-import: refactor parsing of spaces,
2014-06-18).

Signed-off-by: Thalia Archibald <thalia@archibald.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fast-import.c

@@ -2210,7 +2210,7 @@ static int parse_mapped_oid_hex(const char *hex, struct object_id *oid, const ch
  *
  *   idnum ::= ':' bigint;
  *
- * Return the first character after the value in *endptr.
+ * Update *endptr to point to the first character after the value.
  *
  * Complain if the following character is not what is expected,
  * either a space or end of the string.
@@ -2243,8 +2243,8 @@ static uintmax_t parse_mark_ref_eol(const char *p)
 }
 
 /*
- * Parse the mark reference, demanding a trailing space.  Return a
- * pointer to the space.
+ * Parse the mark reference, demanding a trailing space. Update *p to
+ * point to the first character after the space.
  */
 static uintmax_t parse_mark_ref_space(const char **p)
 {