SOF coverage build appears to be caching old fuzzers

Several months ago we switched from a binary called `fuzz_ipc` to two binaries, `sof-ipc3` and `sof-ipc4` as our fuzz targets. The coverage build seems to still fail in reference to the old binaries and an inability to find a corpus despite it not being used for months.

https://oss-fuzz-build-logs.storage.googleapis.com/log-ac6a0524-c8c0-44f4-bd77-aee1fb6af687.txt

@andyross @johnylin76 FYI