enc28j60: Convert HW related printk() to dev_printk()

The debug prints of hardware status and operations will look better
if SPI 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 dev_print(KERN_DEBUG, &spi->dev).
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>