freedreno/a3xx: fix border color swizzle to match texture format desc

freedreno/a3xx: fix border color swizzle to match texture format desc

This is a hack since it uses the texture information together with the
sampler, but I don't see a better way to do it. In OpenGL, there is a
1:1 correspondence.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Rob Clark <robclark@freedesktop.org>