ab8500_fg: match return type of wait_for_completion_timeout

return type of wait_for_completion_timeout is unsigned long not int. as
timeout is used for wait_for_completion_timeout exclusively here its
type is simply changed to unsigned long.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>