net: mdio-mux: add bus name to bus id

In case of DT-configured systems it may be hard to identify the PHY
interrupt in the /proc/interrupts output. Therefore add the name to
the id to make clearer that it's about a device on a muxed mdio bus.
In my case:

Now: mdio_mux-0.e40908ff:08
Before: 0.e40908ff:08

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/00b4bb1e-98f9-b4e7-5549-e095a4701f66@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>