slotmap: Add slotmap_get_id() function to get numeric ID of slot map

Change-Id: Ie476244d9ade30eed9215923275aa82a5d10176f
diff --git a/src/slotmap.c b/src/slotmap.c
index a8874fb..703dd02 100644
--- a/src/slotmap.c
+++ b/src/slotmap.c
@@ -29,6 +29,10 @@
 	return buf;
 }
 
+uint32_t slotmap_get_id(const struct slot_mapping *map)
+{
+	return (map->bank.bank_id << 16) | map->bank.slot_nr;
+}
 
 /* thread-safe lookup of map by client:slot */
 struct slot_mapping *slotmap_by_client(struct slotmaps *maps, const struct client_slot *client)