ath9k_htc: do ani shortcalibratio if we got -ETIMEDOUT

current code will handle -ETIMEDOUT as success which is probalbly wrong.

According to this comment I assume it is safe to handle -ETIMEDOUT as false:
drivers/net/wireless/ath/ath9k/calib.c
290         /*
291          * We timed out waiting for the noisefloor to load, probably due to an
292          * in-progress rx. Simply return here and allow the load plenty of time
293          * to complete before the next calibration interval.  We need to avoid
294          * trying to load -50 (which happens below) while the previous load is
295          * still in progress as this can cause rx deafness. Instead by returning
296          * here, the baseband nf cal will just be capped by our present
297          * noisefloor until the next calibration timer.
298          */

Since no other error wariants are present, this patch is checking only
for (ret <= 0).

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>