In the function weston_log_subscription_printf() we have
a struct weston_log_subscription parameter that in the .c file
is named sub. In the .h, the same parameter is named scope.
This is confusing, since its type is not struct weston_log_scope,
but struct weston_log_subscription.
Rename the parameter in the .h to sub.
Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>