ir3: fix emitting descriptor prefetches at end of preamble

The fix in e7ac1094f6 to emit preamble defs in the correct block would
move the cursor of the builder that is later used to insert descriptor
prefetches, emitting them at the wrong place. Fix this by resetting the
cursor before emitting the prefetches.

Signed-off-by: Job Noorman <jnoorman@igalia.com>
Fixes: e7ac1094f6 ("ir3: rematerialize preamble defs in block dominated by sources")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33399>

src/freedreno/ir3/ir3_nir_opt_preamble.c

@@ -752,6 +752,8 @@ ir3_nir_opt_prefetch_descriptors(nir_shader *nir, struct ir3_shader_variant *v)
                                                   preamble_defs);
          }
 
+         /* ir3_rematerialize_def_for_preamble may have moved the cursor. */
+         b.cursor = nir_after_impl(preamble);
          progress |= emit_descriptor_prefetch(&b, instr, preamble_descs, &state);
 
          if (state.sampler.num_prefetches == MAX_PREFETCHES &&