Replaced tensorrt.tensorrt imports to tensorrt for pip package compatibility

[CorentinJ]

The tensorrt pip package seems not to have tensorrt.tensorrt as module (at least as of version tensorrt==8.6.1.post1), causing 3 imports to fail in the repo. The same members imported from tensorrt.tensorrt are present directly in tensorrt.
It seems that a manual install of Tensor RT (through an archive or .deb package) does not have this problem, but that the members present in tensorrt.tensorrt are equally present in tensorrt.

I haven't gone through the tensorrt changelog to figure out what happened there; but unless this breaks compatibility with older tensorrt versions, changing all tensorrt.tensorrt imports to tensorrt will work with both install methods.