mlxsw: spectrum_router: Adjust mlxsw_sp_inetaddr_vlan_event() coding style

The bridge branch of the dispatch in this function is going to get more
code and will need curly braces. Per the doctrine, that means the whole
if-else chain should get them.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>