i2c: imx: match return type of wait_for_completion_timeout

return type of wait_for_completion_timeout is unsigned long not int.
An appropriate variable of type unsigned long is introduced and the
assignments fixed up.

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