dragonboards: fix boot and vendor_boot partition sizes am: b8380ce018

Original change: https://android-review.googlesource.com/c/device/linaro/dragonboard/+/2781187

Change-Id: I8d33120a809527a982aea0f6d3ad687b5765baa7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>