net/mlx5: Collect command failures data only for known commands

DEVX can issue a general command, which is not used by mlx5 driver.
In case such command is failed, mlx5 is trying to collect the failure
data, However, mlx5 doesn't create a storage for this command, since
mlx5 doesn't use it. This lead to array-index-out-of-bounds error.

Fix it by checking whether the command is known before collecting the
failure data.

Fixes: 34f46ae0

 ("net/mlx5: Add command failures data to debugfs")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>