net/mlx5: E-Switch, Check group pointer before reading bw_share value

[ Upstream commit 5c4e8ae7 ]

If log_esw_max_sched_depth is not supported group pointer of the vport
is NULL. Hence, check the pointer before reading bw_share value.

Fixes: 0fe132ea ("net/mlx5: E-switch, Allow to add vports to rate groups")
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>