[hip] Fix volatile-qualified member function declartion.
[hip] Fix volatile-qualified member function declartion.

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

Change-Id: Id7aaa1953d56151b59e469ef22b9f4280f63bebb

ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP