compositor: Don't ignore --use-pixman for Wayland backend

We loaded the use-pixman configuration value from both the command line
and the configuration file, but completely ignored the former. Make sure
we actually use both.

Tested with all permutations of config/command line.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Tested-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>

compositor/main.c

@@ -2758,7 +2758,7 @@ load_wayland_backend(struct weston_compositor *c,
 	parse_options(wayland_options, ARRAY_LENGTH(wayland_options), argc, argv);
 	config.sprawl = sprawl_;
 	config.fullscreen = fullscreen_;
-	config.use_pixman = use_pixman_config_;
+	config.use_pixman = use_pixman_;
 
 	section = weston_config_get_section(wc, "shell", NULL, NULL);
 	weston_config_section_get_string(section, "cursor-theme",