fix compilation warning: missing field 'readlink' initializer

[TooTallNate]

in Clang:

  CXX(target) Release/obj.target/fuse4js/fuse4js.o
../fuse4js.cc:384:36: warning: missing field 'readlink' initializer [-Wmissing-field-initializers]
  struct fuse_operations ops = { 0 };
                                   ^
1 warning generated.