net/mlx5: qos: Rename rate group 'list' as 'parent_entry'

'list' is not very descriptive, I prefer list membership to clearly
specify which list the entry belongs to. This commit renames the list
entry into the esw groups list as 'parent_entry' to make the code more
readable. This is a no-op change.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>