watchdog: coh901327_wdt: Use dev variable instead of pdev->dev

Use a local dev variable instead of dereferencing pdev->dev several
times in the probe function to make the code easier to read.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>