wifi: mt76: mt7921: reduce the size of MCU firmware download Rx queue

We actually don't need the reserve the 512 entries for the MCU firmware
download Rx queue because the queue was only used in the firmware download
phase to save the most of space and the reduction can significantly help
with reducing latency we spent by ~20% further in resetting the Rx queue
as the device was waking up from deep sleep mode.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/mt7921.h

@@ -12,7 +12,8 @@
 #define MT7921_TX_FWDL_RING_SIZE	128
 
 #define MT7921_RX_RING_SIZE		1536
-#define MT7921_RX_MCU_RING_SIZE		512
+#define MT7921_RX_MCU_RING_SIZE		8
+#define MT7921_RX_MCU_WA_RING_SIZE	512
 
 #define MT7921_EEPROM_SIZE		3584
 #define MT7921_TOKEN_SIZE		8192

drivers/net/wireless/mediatek/mt76/mt7921/pci.c

@@ -200,7 +200,7 @@ static int mt7921_dma_init(struct mt792x_dev *dev)
 	/* Change mcu queue after firmware download */
 	ret = mt76_queue_alloc(dev, &dev->mt76.q_rx[MT_RXQ_MCU_WA],
 			       MT7921_RXQ_MCU_WM,
-			       MT7921_RX_MCU_RING_SIZE,
+			       MT7921_RX_MCU_WA_RING_SIZE,
 			       MT_RX_BUF_SIZE, MT_WFDMA0(0x540));
 	if (ret)
 		return ret;