ath6kl: add debug messages for credit handling

Also take few from htc debug level which are more suitable for credit.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
diff --git a/drivers/net/wireless/ath/ath6kl/debug.h b/drivers/net/wireless/ath/ath6kl/debug.h
index afb747b..491485e 100644
--- a/drivers/net/wireless/ath/ath6kl/debug.h
+++ b/drivers/net/wireless/ath/ath6kl/debug.h
@@ -20,7 +20,7 @@
 #include "hif.h"
 
 enum ATH6K_DEBUG_MASK {
-	/* hole */
+	ATH6KL_DBG_CREDIT	= BIT(0),
 	/* hole */
 	ATH6KL_DBG_WLAN_TX      = BIT(2),     /* wlan tx */
 	ATH6KL_DBG_WLAN_RX      = BIT(3),     /* wlan rx */