Fix diffing CBFS names containing spaces

The first entry in my coreboot.rom is called "cbfs master header", so the previous behaviour of splitting on whitespace would try to extract a non-existent file named "cbfs".

The -k argument to cbfstool print tells it to use "machine-readable" output, which means fields are separated with tabs. I don't think there's any way to handle a name that actually contains a tab character (we can't assume name is the nth last field because the number of fields is variable), so we just have to hope that doesn't come up.