fix gfl export model (#7462)

ppdet/modeling/heads/gfl_head.py

@@ -139,7 +139,7 @@ class DGQP(nn.Layer):
                     axis=2, keepdim=True)], axis=2)
         else:
             stat = prob_topk
-        y = F.relu(self.reg_conv1(stat.reshape([N, -1, H, W])))
+        y = F.relu(self.reg_conv1(stat.reshape([N, 4 * self.reg_topk, H, W])))
         y = F.sigmoid(self.reg_conv2(y))
         return y
 
@@ -435,4 +435,4 @@ class GFLHead(nn.Layer):
         mlvl_scores = paddle.concat(cls_scores, axis=1)
         mlvl_scores = mlvl_scores.transpose([0, 2, 1])
         bbox_pred, bbox_num, _ = self.nms(bboxes, mlvl_scores)
-        return bbox_pred, bbox_num
\ No newline at end of file
+        return bbox_pred, bbox_num