net/mlx5: Devcom, fix error flow in mlx5_devcom_register_device

net/mlx5: Devcom, fix error flow in mlx5_devcom_register_device

In case devcom allocation is failed, mlx5 is always freeing the priv.
However, this priv might have been allocated by a different thread,
and freeing it might lead to use-after-free bugs.
Fix it by freeing the priv only in case it was allocated by the
running thread.

Fixes: fadd59fc50d0 ("net/mlx5: Introduce inter-device communication mechanism")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>