Better fix for GL_UNSIGNED_INT_8_8_8_8[_REV] ...

The GL_RGBA/GL_UNSIGNED_BYTE combination is associated with
GL_RGBA/GL_UNSIGNED_INT_8_8_8_8_REV, but I had the values reversed between
those two combinations and the GL_RGBA/GL_UNSIGNED_INT_8_8_8_8 combination.  By
reversing these, many other format-type combinations no longer looked correct
(e.g. a GL_RED image had solid red components and varying alpha components).

I have now tested this across a larger set of KTX files, and things seem to be
good.