watchdog: light_wdt: Fix warnings

watchdog: light_wdt: Fix warnings

This fixes following warning:

In function 'light_wdt_update_timeout':
drivers/watchdog/light_wdt.c:116:51: warning: implicit
conversion from
'enum light_aon_wdg_func' to 'enum light_aon_misc_func'
[-Wenum-conversion]
light_wdt_msg_hdr_fill(&wdt_dev->msg.hdr,
LIGHT_AON_WDG_FUNC_TIMEOUTSET);

Also, add a 'static' to a static function to suppress other warning.

Change-Id: Ia8f4daa37c58beffc8d0bdb8bcef20108cb282ab
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>