Lint fix: added a missing docstring

Change-Id: If1fb8bb09c538c04e333ccab65a20cff247a504d

Author: Ashutosh Parkhi

python/tvm/relay/testing/tflite.py

@@ -36,6 +36,8 @@ def __init__(self, dtype):
         self.dtype_dict = {}
 
     def create_conv2d_single(self, kernel_shape, strides, padding, dilation, activation):
+        """Returns tf.function that creates TFLite Conv2d layer"""
+
         @tf.function
         def conv2d_single_function(ifm_tensor):
             """Returns TFLite Conv2d layer"""