i2c: img-scb: fixup of wait_for_completion_timeout return handling

Return type of wait_for_completion_timeout is unsigned long not int.
Appropriately typed/named variable are added and assignment fixed up.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Acked-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>