[CINN] Fix test_dot_merger segmentation fault (#55667)

test_dot_merger和test_dot_merger_pass在CI和本地环境中会随机出现segmentation fault错误，导致单测随机挂，经排查后发现是ginac库相关的问题，现避免使用MathIsZero绕过

paddle/cinn/ir/tensor.cc

@@ -553,14 +553,17 @@ ir::Tensor _Tensor_::Reshape(const std::vector<Expr> &shape,
   auto selft = Tensor(const_cast<ir::_Tensor_ *>(this));
 
   {
-    Expr this_num_elements = Expr(1);
-    for (auto &e : this->shape) this_num_elements = this_num_elements * e;
+    int32_t this_num_elements = 1;
+    for (auto &e : this->shape) {
+      this_num_elements = this_num_elements * e.as_int32();
+    }
 
-    Expr num_elements = Expr(1);
-    for (auto &e : shape) num_elements = num_elements * e;
+    int32_t num_elements = 1;
+    for (auto &e : shape) {
+      num_elements = num_elements * e.as_int32();
+    }
 
-    CHECK(MathIsZero(this_num_elements - num_elements))
-        << "number of elements mismatch";
+    CHECK_EQ(this_num_elements, num_elements) << "number of elements mismatch.";
   }
 
   n->name = Context::Global().NewName(name + "_reshape");