!10243 Fix output for Ascend backend of nn.LSTM when dropout is 1.0.

From: @liu_xiao_93
Reviewed-by: @liangchenghui,@wuxuejian
Signed-off-by: @liangchenghui

mindspore/nn/layer/lstm.py

@@ -154,8 +154,12 @@ class LSTM(Cell):
             self.concat_2dim = P.Concat(axis=2)
             self.cast = P.Cast()
             self.shape = P.Shape()
-            if dropout != 0:
-                self.dropout_op = nn.Dropout(float(dropout))
+            if dropout < 0 or dropout > 1:
+                raise ValueError("For LSTM, dropout must be a number in range [0, 1], but got {}".format(dropout))
+            if dropout == 1:
+                self.dropout_op = P.ZerosLike()
+            else:
+                self.dropout_op = nn.Dropout(float(1 - dropout))
             b0 = np.zeros(gate_size, dtype=np.float16)
             self.w_list = []
             self.b_list = []