wayland: Correctly find the keyboard for the keymap

The list of devices was being scanned over incorrectly, causing us to
never actually fetch the keymap from the keyboard, as the keyboard was
the second device in the list, not the first.

This causes us to create a new temporary keymap every time, which is
quite expensive, because it involves parsing the entire XKB
file. Scanning the list correctly will cause us to use the XKB rules
file that was passed to us.

gdk/wayland/gdkdisplay-wayland.c

@@ -514,7 +514,7 @@ _gdk_wayland_display_get_keymap (GdkDisplay *display)
   for (l = list; l; l = l->next)
     {
       GdkDevice *device;
-      device = list->data;
+      device = l->data;
 
       if (gdk_device_get_source (device) != GDK_SOURCE_KEYBOARD)
 	continue;