weston-log: rename the confusing function name weston_compositor_add_log_scope()

There's a function named weston_compositor_add_log_scope()
but it doesn't take a struct weston_compositor argument.

Rename it to weston_log_ctx_add_log_scope(), as
the log_scope is being added to a log_context.

Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>

libweston/weston-log.c

@@ -726,7 +726,8 @@ weston_log_subscription_complete(struct weston_log_subscription *sub)
  * stream. Particularly useful for the weston-debug protocol.
  *
  * @memberof weston_log_scope
- * @sa weston_log_ctx_add_log_scope, weston_log_scope_destroy
+ * @sa weston_log_ctx_add_log_scope, weston_compositor_add_log_scope,
+ * weston_log_scope_destroy
  */
 WL_EXPORT void
 weston_log_scope_complete(struct weston_log_scope *scope)