ath10k: core: match wait_for_completion_timeout return type

Return type of wait_for_completion_timeout is unsigned long not int.
An appropriately named unsigned long is added and the assignments fixed up.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>