mjit.c: fix declaration of ruby_null_device
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62277 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mjit.c: fix declaration of ruby_null_device
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62277 b2dd03c8-39d4-4d8f-98ff-823fe69b080e