dragonboards: fix boot and vendor_boot partition sizes am: b8380ce018 am: eff1beab3f

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

Change-Id: I955f95a798e785202c5cf60e7c37c3ec063021f5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>