net: arc_emac: Fix use after free in arc_mdio_probe()

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

net: arc_emac: Fix use after free in arc_mdio_probe()

If bus->state is equal to MDIOBUS_ALLOCATED, mdiobus_free(bus) will free

the "bus". But bus->name is still used in the next line, which will lead

to a use after free.

We can fix it by putting the name in a local variable and make the

bus->name point to the rodata section "name",then use the name in the

error message without referring to bus to avoid the uaf.