wireless: ath9k: Get rid of timespec conversions

We have interfaces. Remove the open coded cruft. Reduces text size
along with the code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: QCA ath9k Development <ath9k-devel@qca.qualcomm.com>
Cc: John W. Linville <linville@tuxdriver.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>