ath9k_hw: initialize ah->slottime

(u32) -1 is not particularly useful as a slottime default, so even though
the ath9k_hw default should never get used, it's better to pick something
sane here.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hw.c

@@ -408,7 +408,7 @@ static void ath9k_hw_init_defaults(struct ath_hw *ah)
 		AR_STA_ID1_CRPT_MIC_ENABLE |
 		AR_STA_ID1_MCAST_KSRCH;
 	ah->enable_32kHz_clock = DONT_USE_32KHZ;
-	ah->slottime = (u32) -1;
+	ah->slottime = 20;
 	ah->globaltxtimeout = (u32) -1;
 	ah->power_mode = ATH9K_PM_UNDEFINED;
 }