enc28j60: Switch to dev_<level> from pr_<level>

Instead of using open coded printk(KERN_<LEVEL>) switch the driver to use
dev_<level> macros.

Note, the device name will be printed in full, which is beneficial when
more than one card installed on the system.

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