watchdog: iTCO_wdt: Use pdev for platform device and pci_dev for pci device

Use pdev for struct platform_device, pci_dev for struct pci_dev, and dev
for struct device variables to improve consistency.

Remove 'struct platform_device *dev;' from struct iTCO_wdt_private since
it was unused.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>