SaveAsPriorBuffer is not working if dData is offset of hipMalloced buffer

[eddy16112]

In https://github.com/ROCmSoftwarePlatform/hipDNN/blob/master/library/src/hcc_detail/hipdnn_miopen.cpp#L105

    CHECK_HIP(hipMemPtrGetInfo(
        dData, &dPriorSize));  // Get the info of the gradient dx size

If the dData is not directly allocated by hipMalloc, instead, it is part of a pre-allocated memory pool, the dPriorSize obtained is not correct. I think the implementation of SaveAsPriorBuffer only works if dData is allocated by hipMalloc.