staging: dgnc_sysfs: Replace printk(KERN_ERR ) with pr_err()

Fix the following checkpatch warning:
WARNING: Prefer [subsystem eg: netdev]_err([subsystem]dev, ...
then dev_err(dev, ... then pr_err(...  to printk(KERN_ERR ...
Signed-off-by: Ioana Ciornei <ciorneiioana@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_sysfs.c

@@ -75,7 +75,7 @@ void dgnc_create_driver_sysfiles(struct pci_driver *dgnc_driver)
 	rc |= driver_create_file(driverfs, &driver_attr_maxboards);
 	rc |= driver_create_file(driverfs, &driver_attr_pollrate);
 	if (rc)
-		printk(KERN_ERR "DGNC: sysfs driver_create_file failed!\n");
+		pr_err("DGNC: sysfs driver_create_file failed!\n");
 }