mt76: mt7663s: use NULL instead of 0 in sdio code

Fix the following sparse warnings in mt7663s driver:

drivers/net/wireless/mediatek/mt76/mt7615/sdio_mcu.c:78:62: warning:
Using plain integer as NULL pointer
drivers/net/wireless/mediatek/mt76/mt7615/sdio_mcu.c:110:62: warning:
Using plain integer as NULL pointer
drivers/net/wireless/mediatek/mt76/mt7615/sdio_txrx.c:229:64: warning:
Using plain integer as NULL pointer
drivers/net/wireless/mediatek/mt76/mt7615/sdio_txrx.c:263:64: warning:
Using plain integer as NULL pointer

Fixes: a66cbdd6 ("mt76: mt7615: introduce mt7663s support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7615/sdio_mcu.c

@@ -75,7 +75,7 @@ static int mt7663s_mcu_drv_pmctrl(struct mt7615_dev *dev)
 
 	sdio_claim_host(func);
 
-	sdio_writel(func, WHLPCR_FW_OWN_REQ_CLR, MCR_WHLPCR, 0);
+	sdio_writel(func, WHLPCR_FW_OWN_REQ_CLR, MCR_WHLPCR, NULL);
 
 	ret = readx_poll_timeout(mt7663s_read_pcr, dev, status,
 				 status & WHLPCR_IS_DRIVER_OWN, 2000, 1000000);
@@ -107,7 +107,7 @@ static int mt7663s_mcu_fw_pmctrl(struct mt7615_dev *dev)
 
 	sdio_claim_host(func);
 
-	sdio_writel(func, WHLPCR_FW_OWN_REQ_SET, MCR_WHLPCR, 0);
+	sdio_writel(func, WHLPCR_FW_OWN_REQ_SET, MCR_WHLPCR, NULL);
 
 	ret = readx_poll_timeout(mt7663s_read_pcr, dev, status,
 				 !(status & WHLPCR_IS_DRIVER_OWN), 2000, 1000000);

drivers/net/wireless/mediatek/mt76/mt7615/sdio_txrx.c

@@ -226,7 +226,7 @@ void mt7663s_rx_work(struct work_struct *work)
 
 	/* disable interrupt */
 	sdio_claim_host(sdio->func);
-	sdio_writel(sdio->func, WHLPCR_INT_EN_CLR, MCR_WHLPCR, 0);
+	sdio_writel(sdio->func, WHLPCR_INT_EN_CLR, MCR_WHLPCR, NULL);
 	sdio_readsb(sdio->func, &intr, MCR_WHISR, sizeof(struct mt76s_intr));
 	sdio_release_host(sdio->func);
 
@@ -260,7 +260,7 @@ void mt7663s_rx_work(struct work_struct *work)
 
 	/* enable interrupt */
 	sdio_claim_host(sdio->func);
-	sdio_writel(sdio->func, WHLPCR_INT_EN_SET, MCR_WHLPCR, 0);
+	sdio_writel(sdio->func, WHLPCR_INT_EN_SET, MCR_WHLPCR, NULL);
 	sdio_release_host(sdio->func);
 }