meta: Do a massive unindent (and rename) of blitframebuffer_texture().

meta: Do a massive unindent (and rename) of blitframebuffer_texture().

This function is only handling the color case.  We can just unindent as
long as we're willing to do the check for the bit outside of the
function.

v2: Rebase on idr's changes, drop readAtt check that's always non-null
    anyway (it's a pointer into to the statically-allocated attachments
    array in the renderbuffer).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> (v1)