watchdog: mtk_wdt: Cosmetic cleanup of latest changes

This patch cleans up some coding style related issues in the mtk_wtd
driver to make this driver comply again with the U-Boot coding style
standards.

The only minimal functional change is that the timeout parameter is now
passed in (u64) instead of (unsigned int) from mtk_wdt_start() to
mtk_wdt_set_timeout(), preserving the original value.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Shannon Barber <sbarber@dataspeedinc.com>
Cc: Ryder Lee <ryder.lee@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>