libdmabufheap: Do not fallback to ion when dma-buf exists am: d7fd440294 am: 0f1d4f9e68

Original change: https://android-review.googlesource.com/c/platform/system/memory/libdmabufheap/+/2819907

Change-Id: Ib5819e305d5698a4ced632a8bd0086145d31427c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>