i2c: wmt: match return type of wait_for_completion_timeout

return type of wait_for_completion_timeout is unsigned long not int. as
wait_result is only used for wait_for_completion_timeout here the type
is simply changed to unsigned long.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>