[Enhancement] Clearer LUT format error message in ociobakelut #2277

I incorrectly thought that ociobakelut did not support CLF, when in fact the problem was me getting the format specification argument wrong.

The error message said "File format does not support baking" leading me to believe I had specified a format which was valid, but which could not be used for ociobakelut.

It would have been clearer if the error had said something like "Unrecognised file format".