[hip] Fix volatile-qualified member function declartion.

- It should be a volatile-qualified member function instead of returning
  volatile type.

Change-Id: Id7aaa1953d56151b59e469ef22b9f4280f63bebb

include/hip/hcc_detail/hip_fp16.h

@@ -229,7 +229,7 @@ THE SOFTWARE.
             __host__ __device__
             operator __half_raw() const { return __half_raw{data}; }
             __host__ __device__
-            operator volatile __half_raw() const volatile
+            operator __half_raw() const volatile
             {
                 return __half_raw{data};
             }