With clang 15, the following -Werror warning is produced:
sys/dev/mlx5/mlx5_core/mlx5_fs_tree.c:1408:15: error: variable 'candidate_group_num' set but not used [-Werror,-Wunused-but-set-variable]
unsigned int candidate_group_num = 0;
^
The 'candidate_group_num' variable appears to have been a debugging aid
that has never been used for anything, so remove it.
MFC after: 3 days