src: fix typos in node_lttng_provider.h

Is a semver-breaking change

Refs: https://github.com/nodejs/node/pull/11189#discussion_r99509433
PR-URL: https://github.com/nodejs/node/pull/11723


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>