gallivm/sample: fix sampling indirect from vertex shaders
What does this MR do and why?
gallivm/sample: fix sampling indirect from vertex shaders
When doing indirect sampling, we just fetch one value per lane,
but type.length == 1 caused num_quads to be 0 which caused things
to crash.
Fixes dEQP-GLES31.functional.shaders.opaque_type_indexing.sampler.uniform.vertex.sampler2d
Cc: mesa-stable