RDMA/mlx5: Fix MR cache debugfs error in IB representors mode

RDMA/mlx5: Fix MR cache debugfs error in IB representors mode

Block MR cache debugfs creation for IB representor flow as MR cache shouldn't be used
at all in that mode. As part of this change, add missing debugfs cleanup in error path
too.

This change fixes the following debugfs errors:

 bond0: (slave enp8s0f1): Enslaving as a backup interface with an up link
 mlx5_core 0000:08:00.0: lag map: port 1:1 port 2:1
 mlx5_core 0000:08:00.0: shared_fdb:1 mode:queue_affinity
 mlx5_core 0000:08:00.0: Operation mode is single FDB
 debugfs: Directory '2' with parent '/' already present!
...
 debugfs: Directory '22' with parent '/' already present!

Fixes: 73d09b2fe833 ("RDMA/mlx5: Introduce mlx5r_cache_rb_key")
Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
Link: https://lore.kernel.org/r/482a78c54acbcfa1742a0e06a452546428900ffa.1675328463.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>