staging/gdm72xx: Use netdev_ or pr_ printks in gdm_wimax.c

staging/gdm72xx: Use netdev_ or pr_ printks in gdm_wimax.c

fixed below checkpatch warnings.
- WARNING: Prefer netdev_err(netdev, ... then dev_err(dev, ... then pr_err(...  to printk(KERN_ERR ...
- WARNING: Prefer netdev_emerg(netdev, ... then dev_emerg(dev, ... then pr_emerg(...  to printk(KERN_EMERG ...
- WARNING: Prefer netdev_info(netdev, ... then dev_info(dev, ... then pr_info(...  to printk(KERN_INFO ...

and add pr_fmt.

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