[NFC] polish colossalai/kernel/cuda_native/csrc/kernels/include/softmax.h code style (#964)

colossalai/kernel/cuda_native/csrc/kernels/include/softmax.h

@@ -10,7 +10,8 @@
 
 using namespace std;
 
-template <typename T> class Softmax {
+template <typename T>
+class Softmax {
  public:
   struct Config {
     size_t nhead;