enc28j60: Convert printk() to netdev_printk()

The debug prints of network operations will look better if network
device name is printed. The benefit of that is a possibility to distinguish
the actual hardware when more than one is installed on the system.

Convert appropriate printk(KERN_DEBUG) to netdev_print(KERN_DEBUG, ndev).

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>