!4894 Fix minor bugs in transformed distribution

Merge pull request !4894 from peixu_ren/custom_bijector

mindspore/nn/probability/distribution/transformed_distribution.py

@@ -105,7 +105,7 @@ class TransformedDistribution(Distribution):
         return self.exp(self._log_prob(*args, **kwargs))
 
     def _sample(self, *args, **kwargs):
-        org_sample = self.distribution("sample", shape)
+        org_sample = self.distribution("sample", *args, **kwargs)
         return self.bijector("forward", org_sample)
 
     def _mean(self, *args, **kwargs):
@@ -114,6 +114,6 @@ class TransformedDistribution(Distribution):
             This function maybe overridden by derived class.
         """
         if not self.is_linear_transformation:
-            raise_not_impl_error(mean)
+            raise_not_impl_error("mean")
 
         return self.bijector("forward", self.distribution("mean"))