tu: Fix xfb when there is a hole at the end

We were handling the case where we had an unassigned output in the
middle of the outputs array, but v->outputs can be smaller than the
shader's info.num_outputs when an output at the end isn't assigned. This
lead to us reading garbage after the end, and assuming that it
corresponded to r0.x and overwriting the xfb entry for some other random
output with the unassigned output's entry.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12310>

src/freedreno/ci/deqp-freedreno-a630-fails.txt

@@ -281,6 +281,3 @@ dEQP-VK.ssbo.layout.random.all_shared_buffer.5,Fail
 dEQP-VK.ssbo.layout.random.nested_structs_arrays.0,Fail
 dEQP-VK.ssbo.layout.random.nested_structs_arrays.17,Fail
 dEQP-VK.ssbo.layout.random.scalar.19,Fail
-
-# "Mismatch at offset 0 expected -89 received 0 (elemNdx=0 vecNdx=0 compNdx=0)"
-dEQP-VK.transform_feedback.fuzz.various_buffers.buffers100_instance_array_vertex,Fail

src/freedreno/vulkan/tu_pipeline.c

@@ -726,8 +726,8 @@ tu6_setup_streamout(struct tu_cs *cs,
       unsigned k = out->register_index;
       unsigned idx;
 
-      /* Skip it, if there's an unused reg in the middle of outputs. */
-      if (v->outputs[k].regid == INVALID_REG)
+      /* Skip it, if it's an output that was never assigned a register. */
+      if (k >= v->outputs_count || v->outputs[k].regid == INVALID_REG)
          continue;
 
       ncomp[out->output_buffer] += out->num_components;