watchdog: kempld_wdt: Add __user annotation

Added __user annotation to fix the following sparse warnings.
Also, it makes 'kempld_prescaler' static because it is used
only in this file.

drivers/watchdog/kempld_wdt.c:70:11: warning: symbol 'kempld_prescaler' was not declared. Should it be static?
drivers/watchdog/kempld_wdt.c:364:23: warning: incorrect type in initializer (different address spaces)
drivers/watchdog/kempld_wdt.c:364:23:    expected int const [noderef] <asn:1>*register __p
drivers/watchdog/kempld_wdt.c:364:23:    got int *<noident>

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