Temporarily revert ipu config change

ipu_config.json

@@ -14,6 +14,6 @@
     "executable_cache_dir": "./exe_cache",                                                                                       
   
     "ipus_per_replica": 4,                                                                                                       
-    "layers_per_ipu": [3, 3, 3, 3],                                                                                              
+    "layers_per_ipu": [0, 3, 4, 5],                                                                                              
     "matmul_proportion": [0.25, 0.25, 0.25, 0.25]
  }