d3d12: do not use undefined LOD for texcoords

This instruction is supported on all NIR based drivers, but without it u_blitter will make some pretty bad choices, and instead use an undefined LOD.

This should IMO be fixed properly upstream, and I have a merge-request open for that. In the mean-time, let's paper over this in the driver so we can move on.

This fixes a case for me where the following two Khronos Confidental CTS cases are run back to back:

GTF-GL33.gtf30.GL3Tests.framebuffer_blit.framebuffer_blit_error_blitframebuffer_multisampled_framebuffers_different_formats GTF-GL33.gtf30.GL3Tests.framebuffer_blit.framebuffer_blit_functionality_nearest_filter_color_blit