generator.h: use GET_STATE_TO
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49048 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
generator.h: use GET_STATE_TO
macro, instead of TypedData_Get_Struct directly.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49048 b2dd03c8-39d4-4d8f-98ff-823fe69b080e