libc_fs: Use priority higher than libc_vfs

This way, we make sure that libc_fs is used if both plugins are
present, which happens during the transition to libc_vfs.

libports/src/lib/libc_fs/plugin.cc

@@ -211,8 +211,10 @@ class Plugin : public Libc::Plugin
 
 		/**
 		 * Constructor
+		 *
+		 * Use priority 1 to override libc_vfs.
 		 */
-		Plugin() { }
+		Plugin() : Libc::Plugin(1) { }
 
 		~Plugin() { }