anv: Fix output of INTEL_DEBUG=bat for chained batches

The anv_batch_bo contents are linked one to another, and when printing
we have to start with the first of those.  Since in `u_vector` new
elements are added to the head, to get the first element we need the
vector's tail.

Fixes: 32ffd90002 ("anv: add support for INTEL_DEBUG=bat")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/vulkan/anv_batch_chain.c

@@ -1732,7 +1732,7 @@ anv_cmd_buffer_execbuf(struct anv_device *device,
 
    if (cmd_buffer) {
       if (unlikely(INTEL_DEBUG & DEBUG_BATCH)) {
-         struct anv_batch_bo **bo = u_vector_head(&cmd_buffer->seen_bbos);
+         struct anv_batch_bo **bo = u_vector_tail(&cmd_buffer->seen_bbos);
 
          device->cmd_buffer_being_decoded = cmd_buffer;
          gen_print_batch(&device->decoder_ctx, (*bo)->bo.map,