Fix typo in ensure no password script

The current version always fails - and generates false positives. (This is not
the version that is on the live signer, so we are good.)

Change-Id: I7cb14cdcaf4d96bc2911e596224ead9a3738aa18

BUG=chromium-os:1459
TEST=manually tested

Review URL: http://codereview.chromium.org/6322006

scripts/image_signing/ensure_no_password.sh

@@ -19,7 +19,7 @@ IMAGE=$1
 ROOTFS=$(make_temp_dir)
 mount_image_partition_ro "$IMAGE" 3 "$ROOTFS"
 
-if ! no_chronos_password $rootfs; then
+if ! no_chronos_password $ROOTFS; then
     echo "chronos password is set! Shouldn't be for release builds."
     exit 1
 fi