platfrom -> platform

This changes a struct name. The related code is conditionally
compiled and won't work because the include file linux/gpio-decoder.h
is missing, so removing this code would be an even better solution.

If the missing include file is added, it must fix the spelling, too.
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>