net/mlx5: Refactor devcom to return NULL on failure

Devcom device and component registration isn't always critical to the
functionality of the caller, hence the registration can fail and we can
continue working with an ERR_PTR value saved inside a variable.

In order to avoid that make sure all devcom failures return NULL.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1761136182-918470-4-git-send-email-tariqt@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>