[Eager] polish bmm api (#49823)

python/paddle/tensor/linalg.py

@@ -1557,6 +1557,9 @@ def bmm(x, y, name=None):
             #          [60., 60.]]])
 
     """
+    if in_dygraph_mode():
+        return _C_ops.bmm(x, y)
+    else:
         x_shape = x.shape
         y_shape = y.shape
         if not len(x_shape) == len(y_shape) == 3:
@@ -1577,10 +1580,6 @@ def bmm(x, y, name=None):
                     x_shape, y_shape
                 )
             )
-
-    if in_dygraph_mode():
-        return _C_ops.bmm(x, y)
-    else:
         helper = LayerHelper('bmm', **locals())
         out = helper.create_variable_for_type_inference(dtype=x.dtype)
         helper.append_op(