watchdog: ts72xx_wdt: make 'ts72xx_wdt_pdev' static

Make 'ts72xx_wdt_pdev' static, because it is used only in this
file. It also fixes the following sparse warning.

  warning: symbol 'ts72xx_wdt_pdev' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/ts72xx_wdt.c

@@ -61,7 +61,7 @@ struct ts72xx_wdt {
 	struct platform_device *pdev;
 };
 
-struct platform_device *ts72xx_wdt_pdev;
+static struct platform_device *ts72xx_wdt_pdev;
 
 /*
  * TS-72xx Watchdog supports following timeouts (value written