ath9k: add a helper to get the string representation of ath_bus_type

This can be used when the ath_bus_type has to be presented in a log
message or firmware filename.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
diff --git a/drivers/net/wireless/ath/ath.h b/drivers/net/wireless/ath/ath.h
index da7a7c8..f3f2784 100644
--- a/drivers/net/wireless/ath/ath.h
+++ b/drivers/net/wireless/ath/ath.h
@@ -327,4 +327,10 @@ static inline const char *ath_opmode_to_string(enum nl80211_iftype opmode)
 }
 #endif
 
+extern const char *ath_bus_type_strings[];
+static inline const char *ath_bus_type_to_string(enum ath_bus_type bustype)
+{
+	return ath_bus_type_strings[bustype];
+}
+
 #endif /* ATH_H */