ath9k_htc: match wait_for_completion_timeout return type

Return type of wait_for_completion_timeout is unsigned long not int.
As time_left is exclusively used for wait_for_completion_timeout here its
type is simply changed to unsigned long.

API conformance testing for completions with coccinelle spatches are being
used to locate API usage inconsistencies:
./drivers/net/wireless/ath/ath9k/htc_hst.c:171
	int return assigned to unsigned long
./drivers/net/wireless/ath/ath9k/htc_hst.c:277
	int return assigned to unsigned long
./drivers/net/wireless/ath/ath9k/htc_hst.c:206
	int return assigned to unsigned long

Patch was compile tested with x86_64_defconfig + CONFIG_ATH_CARDS=m,
CONFIG_ATH9K_HTC=m

Patch is against 4.1-rc3 (localversion-next is -next-20150514)

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