obs-x264: Fix settings string typo

This is why macros should be used for settings strings.

(Commit edited and formatted by Jim: separated this code from the
following commit, and gave it a proper commit message)

Closes jp9000/obs-studio#567

plugins/obs-x264/obs-x264.c

@@ -152,7 +152,7 @@ static bool rate_control_modified(obs_properties_t *ppts, obs_property_t *p,
 	obs_property_set_visible(p, !rc_crf);
 	p = obs_properties_get(ppts, "use_bufsize");
 	obs_property_set_visible(p, !rc_crf);
-	p = obs_properties_get(ppts, "buffse_size");
+	p = obs_properties_get(ppts, "buffer_size");
 	obs_property_set_visible(p, !rc_crf);
 	return true;
 }