net/mlx5: E-switch, Don't update group if qos is not enabled

Currently, qos group will be updated and qos will be enabled when
unregistering devlink port. Actually no need to update group if qos
is not enabled.

Add a check to prevent unnecessary enabling and disabling qos for
every port.

Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Dmytro Linkin <dlinkin@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>