use ext4 instead of yaffs

This is needed to allow the emulator to use ext4 images.

Bug: https://code.google.com/p/android/issues/detail?id=38561
Change-Id: I02fde6382ad67cf7f4f3b695396841f70bb9301d
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 5206cd1..065a823 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -134,10 +134,10 @@
 on fs
 # mount mtd partitions
     # Mount /system rw first to give the filesystem a chance to save a checkpoint
-    mount yaffs2 mtd@system /system
-    mount yaffs2 mtd@system /system ro remount
-    mount yaffs2 mtd@userdata /data nosuid nodev
-    mount yaffs2 mtd@cache /cache nosuid nodev
+    mount ext4 mtd@system /system
+    mount ext4 mtd@system /system ro remount
+    mount ext4 mtd@userdata /data nosuid nodev
+    mount ext4 mtd@cache /cache nosuid nodev
 
 on post-fs
     # once everything is setup, no need to modify /