loader: Call down chain for vkEnumerateDeviceExtensionProperties

This allows layers to filter device extensions.
diff --git a/loader/loader.h b/loader/loader.h
index addfc01..829b2d1 100644
--- a/loader/loader.h
+++ b/loader/loader.h
@@ -185,8 +185,7 @@
     VkPhysicalDevice phys_dev;          // object from ICD
     /*
      * Fill in the cache of available device extensions from
-     * this physical device. This cache will be used to satisfy
-     * calls to EnumerateDeviceExtensionProperties
+     * this physical device. This cache can be used during CreateDevice
      */
     struct loader_extension_list device_extension_cache;
 };