Convert all scales to int32_t

The type changed in the protocol, so update weston for this.
diff --git a/clients/desktop-shell.c b/clients/desktop-shell.c
index 40dd1dd..51ce3ec 100644
--- a/clients/desktop-shell.c
+++ b/clients/desktop-shell.c
@@ -1115,7 +1115,7 @@
 static void
 output_handle_scale(void *data,
                     struct wl_output *wl_output,
-                    uint32_t scale)
+                    int32_t scale)
 {
 	struct output *output = data;