staging/comedi: Use pr_ or dev_ printks in drivers/serial2002.c

fixed below checkpatch warning.
- WARNING: Prefer netdev_err(netdev, ... then dev_err(dev, ... then pr_err(...  to printk(KERN_ERR ...

and added pr_fmt.
Signed-off-by: YAMANE Toshiaki <yamanetoshi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/serial2002.c

@@ -31,6 +31,8 @@ Status: in development
 
 */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include "../comedidev.h"
 
 #include <linux/delay.h>
@@ -272,7 +274,7 @@ static struct serial_data serial_read(struct file *f, int timeout)
 
 		length++;
 		if (data < 0) {
-			printk(KERN_ERR "serial2002 error\n");
+			pr_err("Failed to read serial.\n");
 			break;
 		} else if (data & 0x80) {
 			result.value = (result.value << 7) | (data & 0x7f);
@@ -346,7 +348,7 @@ static int serial_2002_open(struct comedi_device *dev)
 	devpriv->tty = filp_open(port, O_RDWR, 0);
 	if (IS_ERR(devpriv->tty)) {
 		result = (int)PTR_ERR(devpriv->tty);
-		printk(KERN_ERR "serial_2002: file open error = %d\n", result);
+		dev_err(dev->class_dev, "file open error = %d\n", result);
 	} else {
 		struct config_t {