net/mlx5: SF, Drain health before removing device

There is no point in recovery during device removal. Also, if health
work started need to wait for it to avoid races and NULL pointer
access.

Hence, drain health WQ before removing device.

Fixes: 1958fc2f

 ("net/mlx5: SF, Add auxiliary device driver")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>