soc/tegra: Watch wait_for_completion_timeout() return type

The return type of the wait_for_completion_timeout() function is not int
but unsigned long. An appropriately named unsigned long is added and the
assignment fixed up.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>