platform: generic-arm64: Adjust hypervisor_mmio_map_region error handling am: 13a8ea12a7

Original change: https://android-review.googlesource.com/c/trusty/lk/trusty/+/3518512

Change-Id: I9c79fcef8df7b86f21acb6cc2557d2f719917a65
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>