net: dsa: mv88e6xxx: enable .rmu_disable() on Topaz

Commit 9e5baf9b

 ("net: dsa: mv88e6xxx: add RMU disable op")
introduced .rmu_disable() method with implementation for several models,
but forgot to add Topaz, which can use the Peridot implementation.

Use the Peridot implementation of .rmu_disable() on Topaz.

Signed-off-by: Marek Behún <kabel@kernel.org>
Fixes: 9e5baf9b

 ("net: dsa: mv88e6xxx: add RMU disable op")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>