Gemm test return value (#148)

* Add return value

* Replace _Float16 to ck::half_t

* A test should return 0 if success and return non-zero if fail

test/gemm/gemm_bf16.cpp

@@ -113,4 +113,5 @@ int main()
     }
 
     std::cout << "TestGemm ..... " << (res ? "SUCCESS" : "FAILURE") << std::endl;
+    return res ? 0 : 1;
 }