✏️ Fixed doc error

Author: PommesPeter

python/paddle/tensor/math.py

@@ -7189,7 +7189,7 @@ def signbit(x, name=None):
 
             >>> import paddle
             >>> x = paddle.to_tensor([1.1, -2.1, 0., 2.5, -0.0], dtype='float32')
-            >>> res = paddle.signbit(x, y)
+            >>> res = paddle.signbit(x)
             >>> print(res)
             Tensor(shape=[4], dtype=bool, place=Place(cpu), stop_gradient=True,
             [False , True, False, False, True])
@@ -7198,7 +7198,7 @@ def signbit(x, name=None):
             :name: signbit-example-2
 
             >>> x = paddle.to_tensor([-5, -2, 3], dtype='int32')
-            >>> res = paddle.signbit(x, y)
+            >>> res = paddle.signbit(x)
             >>> print(res)
             Tensor(shape=[3], dtype=bool, place=Place(cpu), stop_gradient=True,
             [True. , True , False])