watchdog: update geodewdt for new MFGPT API

Update to the new cs5535_mfgpt* API.  The geode-specific wording should
eventually be dropped from this driver...

Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>