Minor fixes to ensure cpp demo builds on OpenCV 4.x, TensorRT 8.x

Fixed cpp demo build on OpenCV 4.x (BGR2RGB has been renamed)
Fixed TensorRT version info in FindTensorRT.cmake (version info has moved to a separate header).

Fixed build error caused by logger (Logger, https://forums.developer.nvidia.com/t/looser-throw-specifier-for-virtual-void-logger-log/187963)

**mmdetection-to-tensorrt/demo/cpp/main.cpp:21:10: error: looser throw specifier for ‘virtual void Logger::log(nvinfer1::ILogger::Severity, const char*)’

Builds successfully on TensorRT 8.2.1, Opencv 4.5.2

grimoire / mmdetection-to-tensorrt

Minor fixes to ensure cpp demo builds on OpenCV 4.x, TensorRT 8.x #100