fix: use absolute path for CUDA directory detection
The capability detection was using a relative path 'usr/local/cuda-13'
which doesn't work when LocalAI is run from a different working directory.
This caused whisper (and other backends) to fail on CUDA-13 containers
because the system incorrectly detected 'nvidia' capability instead of
'nvidia-cuda-13', leading to wrong backend selection (cuda12-whisper
instead of cuda13-whisper).
Fixes: https://github.com/mudler/LocalAI/issues/8033
Co-authored-by: localai-bot <localai-bot@users.noreply.github.com>