watchdog: imx2: Constify struct regmap_config and watchdog_ops

The regmap_config struct may be const because it is not modified by the
driver and regmap_init() accepts pointer to const. Make struct
watchdog_ops const as well.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>