ath9k_htc: Handle device unplug properly

When the USB device has been unplugged, there is
no point in trying to send commands to the target.
Fix this by denying all WMI commands in such a case.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/htc.h b/drivers/net/wireless/ath/ath9k/htc.h
index c765ff4..b771e20 100644
--- a/drivers/net/wireless/ath/ath9k/htc.h
+++ b/drivers/net/wireless/ath/ath9k/htc.h
@@ -329,6 +329,7 @@
 #define OP_ASSOCIATED     BIT(8)
 #define OP_ENABLE_BEACON  BIT(9)
 #define OP_LED_DEINIT     BIT(10)
+#define OP_UNPLUGGED      BIT(11)
 
 struct ath9k_htc_priv {
 	struct device *dev;