libvndksupport: log sphal namespace fallback

If someone is trying to use the sphal namespace, but it
isn't available, we should probably fix this code or add an
sphal namespace there or similar. Add log for more clarity.

Bug: N/A
Test: boot cuttlefish, this doesn't get logged
Change-Id: I2fd2cddc90f529218c99ede8daf2891d84ceb94c