fix resnet on CPU

examples/ResNet/imagenet-resnet.py

@@ -84,9 +84,9 @@ def get_data(train_or_test):
 
 
 def get_config(fake=False, data_format='NCHW'):
-    nr_gpu = get_nr_gpu()
-    BATCH_SIZE = TOTAL_BATCH_SIZE // nr_gpu
-    logger.info("Running on {} GPUs. Batch size per GPU: {}".format(nr_gpu, BATCH_SIZE))
+    nr_tower = max(get_nr_gpu(), 1)
+    BATCH_SIZE = TOTAL_BATCH_SIZE // nr_tower
+    logger.info("Running on {} towers. Batch size per tower: {}".format(nr_tower, BATCH_SIZE))
 
     if fake:
         dataset_train = dataset_val = FakeData(
@@ -109,7 +109,7 @@ def get_config(fake=False, data_format='NCHW'):
         ],
         steps_per_epoch=5000,
         max_epoch=110,
-        nr_tower=nr_gpu
+        nr_tower=nr_tower
     )