smsc911x: Do not use netdev_dbg() when device is not registered

With debug enabled we get the following message:

smsc911x smsc911x (unregistered net_device): couldn't get clock -2

As the device has not been registered at this point, it is better to use
dev_dbg() instead of netdev_dbg().

CC: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>

Suggested-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>