net/mlx5: Pair mutex_destory with mutex_init for rate limit table

Add missing mutex_destroy() to pair with mutex_init().

This should be done only when table is initialized, hence perform
mutex_init() only when table is initialized.

Signed-off-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>