CVE-2024-40921 net: bridge: mst: pass vlan group directly to br_mst_vlan_set_state

In the Linux kernel, the following vulnerability has been resolved:

net: bridge: mst: pass vlan group directly to br_mst_vlan_set_state

Pass the already obtained vlan group pointer to br_mst_vlan_set_state()
instead of dereferencing it again. Each caller has already correctly
dereferenced it for their context. This change is required for the
following suspicious RCU dereference fix. No functional changes
intended.