fix jetson build break caused by https://github.com/microsoft/onnxruntime/pull/12949 (#13310)
https://github.com/microsoft/onnxruntime/pull/12949 breaks Jetson/ARM
builds due to
invalid narrowing conversion from "char" to "signed char". (on ARM, char
is unsigned)
This was reported by
https://github.com/microsoft/onnxruntime/issues/13285#issuecomment-1276122505