re.c: count associated Regexp object in MatchData#hash

Don't discard the hash value computed for the regexp object. It seems it
was simply missed out in r24754, when MatchData#hash was initially
implemented.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56962 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

re.c

@@ -2950,7 +2950,7 @@ match_hash(VALUE match)
     const struct re_registers *regs;
     st_index_t hashval = rb_hash_start(rb_str_hash(RMATCH(match)->str));
 
-    rb_hash_uint(hashval, reg_hash(RMATCH(match)->regexp));
+    hashval = rb_hash_uint(hashval, reg_hash(RMATCH(match)->regexp));
     regs = RMATCH_REGS(match);
     hashval = rb_hash_uint(hashval, regs->num_regs);
     hashval = rb_hash_uint(hashval, rb_memhash(regs->beg, regs->num_regs * sizeof(*regs->beg)));