pass test for lstm op

test=develop

paddle/fluid/operators/math/detail/lstm_kernel.h

@@ -37,6 +37,7 @@ class lstm {
     *value_ig = activation(*value_ig + (*prev_state) * (*checkI), active_gate);
     *value_fg = activation(*value_fg + (*prev_state) * (*checkF), active_gate);
     *state = (*value_in) * (*value_ig) + (*prev_state) * (*value_fg);
+
     if (*cell_clip > 0.0) {
       if (*state < -1.0 * (*cell_clip)) {
         *state = -1.0 * (*cell_clip);
@@ -73,6 +74,7 @@ class lstm {
         active_gate);
     *state = _mm256_add_ps(_mm256_mul_ps(*value_in, *value_ig),
                            _mm256_mul_ps(*prev_state, *value_fg));
+
     if (*cell_clip > 0.0f) {
       __m256 min = _mm256_set1_ps(0.0f - *cell_clip);
       __m256 max = _mm256_set1_ps(*cell_clip);
@@ -114,7 +116,12 @@ class lstm {
             activation((*output_grad) * (*value_og), *state_atv, active_state) +
             (*grad_og) * (*checkO);
       }
+    } else {
+      *state_grad +=
+          activation((*output_grad) * (*value_og), *state_atv, active_state) +
+          (*grad_og) * (*checkO);
     }
+
     *grad_in = activation((*state_grad) * (*value_ig), *value_in, active_node);
     *grad_ig = activation((*state_grad) * (*value_in), *value_ig, active_gate);
     *grad_fg =