draw/texture: handle mip_offset[0] being != 0 for layered textures.
draw/texture: handle mip_offset[0] being != 0 for layered textures.
When llvmpipe adds on a layer it uses mip_offset[0] for it, so it
should still be respected even for multisample.
Fixes KHR-GL45.texture_view.view_sampling
Fixes: 839045bcc840 ("gallivm/lp: merge sample info into normal info")