i2c: cadence: fixup wait_for_completion_timeout return handling

return type of wait_for_completion_timeout is unsigned long not int. The
return variable is renamed to make the timeout condition clearly readable
and the type adjusted to unsigned long.

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