rocker: print switch ID consistent with phys_switch_id sysfs node

On sucessful probe, driver prints the switch ID.  This patch changes the
format of the printed ID to match what's used in sysfs phys_switch_id node.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>