compile.c: assignment result of aset_with

* compile.c (iseq_compile_each): result of assignment should be
  its rhs instead of returned value from a method.
  [ruby-core:60071] [Bug #9448]

git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/trunk@44705 b2dd03c8-39d4-4d8f-98ff-823fe69b080e