Fix a command to get android.boot.dtbo_index am: 8b45162bf6

Original change: https://android-review.googlesource.com/c/platform/test/vts/+/2385772

Change-Id: Id9689e802b1c485bc66b8d32c210b28cd2aa1216
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>