vkformat: Revert the inversion of RGB mapping according to its transfer type

After the merge of !5288 (merged) the test element_vkcolorconvert started to fail because it couldn't use ARGB format.

Digging on it I realized that I did a wrong code review (sorry!), because the semantics of mapping formats is the first column is for the non-sRGB formats and the second column for the sRGB transfer formats, in the case of RGB.

And now the old and venerable libs_vkformat unit test returned to its original checked values.

Also are other two (almost) cosmetic changes.

cc: @ystreet

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