fix sd-ext backup and restore.

Change-Id: I346724f231bb29df2c0fa833df420620ab1be1b4
diff --git a/nandroid.c b/nandroid.c
index df33cee..7afdc81 100644
--- a/nandroid.c
+++ b/nandroid.c
@@ -198,7 +198,7 @@
     {
         if (0 != ensure_path_mounted("/sd-ext"))
             ui_print("Could not mount sd-ext. sd-ext backup may not be supported on this device. Skipping backup of sd-ext.\n");
-        else if (0 != (ret = nandroid_backup_partition(backup_path, "SDEXT:")))
+        else if (0 != (ret = nandroid_backup_partition(backup_path, "/sd-ext")))
             return ret;
     }