net: dsa: update dsa_of_{probe, remove} to use a device pointer

In preparation for allowing a different mechanism to register DSA switch
devices and driver, update dsa_of_probe and dsa_of_remove to take a
struct device pointer since neither of these two functions uses the
struct platform_device pointer.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>