mt76: mt7603: fix ED/CCA monitoring with single-stream devices

Do not use the RSSI values of the unavailable chain
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7603/mac.c

@@ -1631,9 +1631,13 @@ mt7603_edcca_check(struct mt7603_dev *dev)
 	if (rssi0 > 128)
 		rssi0 -= 256;
 
+	if (dev->mphy.antenna_mask & BIT(1)) {
 		rssi1 = FIELD_GET(MT_AGC_41_RSSI_1, val);
 		if (rssi1 > 128)
 			rssi1 -= 256;
+	} else {
+		rssi1 = rssi0;
+	}
 
 	if (max(rssi0, rssi1) >= -40 &&
 	    dev->ed_strong_signal < MT7603_EDCCA_BLOCK_TH)