draw/llvm: fix big-endian mask adjusting

draw/llvm: fix big-endian mask adjusting

This code was broken, but it worked by accident, as the
pad and the edgeflag were reversed, however when Roland
removed the cliptest field back in 2015, he stopped copying
the pad which actually stopped copy the edgeflag.

Fix the function to actually copy the edgeflag.

Fixes: 1b22815af624 ("draw: don't pretend have_clipdist is per-vertex")
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5679>