So far for the formats E5B9G9R9_UFLOAT_PACK32 and
B10G11R11_UFLOAT_PACK32 we were using a XYZW swizzle. But from Vulkan
spec those are three-component, without alpha, formats. So we should
use XYZ1 instead, as we were already doing for other three-component
formats.

Curiously the only case where this raised a problem were when using
clamp to border with transparent black. This change allows us to
remove the code that handled only that specific case.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <mesa/mesa!7355>