ath9k: downgrade assert in rc.c for invalid rate

The case where no vaid rate is found should not happen now
but to help debugging and downgrade this to a warn.
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -741,10 +741,18 @@ static u8 ath_rc_ratefind_ht(struct ath_softc *sc,
 	if (rate > (ath_rc_priv->rate_table_size - 1))
 		rate = ath_rc_priv->rate_table_size - 1;
 
-	ASSERT((rate_table->info[rate].valid &&
-		(ath_rc_priv->ht_cap & WLAN_RC_DS_FLAG)) ||
-	       (rate_table->info[rate].valid_single_stream &&
-		!(ath_rc_priv->ht_cap & WLAN_RC_DS_FLAG)));
+	if (rate_table->info[rate].valid &&
+	    (ath_rc_priv->ht_cap & WLAN_RC_DS_FLAG))
+		return rate;
+
+	if (rate_table->info[rate].valid_single_stream &&
+	    !(ath_rc_priv->ht_cap & WLAN_RC_DS_FLAG));
+		return rate;
+
+	/* This should not happen */
+	WARN_ON(1);
+
+	rate = ath_rc_priv->valid_rate_index[0];
 
 	return rate;
 }