mt76: mt7615: fix endianness warning in mt7615_mac_write_txwi

Fix the following sparse warning in mt7615_mac_write_txwi routine:
drivers/net/wireless/mediatek/mt76/mt7615/mac.c:758:17:
	warning: incorrect type in assignment
	expected restricted __le32 [usertype]
	got unsigned long

Fixes: 04b8e659 ("mt76: add mac80211 driver for MT7615 PCIe-based chipsets")
Fixes: d4bf77bd ("mt76: mt7615: introduce mt7663u support to mt7615_write_txwi")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -755,12 +755,15 @@ int mt7615_mac_write_txwi(struct mt7615_dev *dev, __le32 *txwi,
 	if (info->flags & IEEE80211_TX_CTL_NO_ACK)
 		txwi[3] |= cpu_to_le32(MT_TXD3_NO_ACK);
 
-	txwi[7] = FIELD_PREP(MT_TXD7_TYPE, fc_type) |
-		  FIELD_PREP(MT_TXD7_SUB_TYPE, fc_stype) |
-		  FIELD_PREP(MT_TXD7_SPE_IDX, 0x18);
-	if (!is_mmio)
-		txwi[8] = FIELD_PREP(MT_TXD8_L_TYPE, fc_type) |
-			  FIELD_PREP(MT_TXD8_L_SUB_TYPE, fc_stype);
+	val = FIELD_PREP(MT_TXD7_TYPE, fc_type) |
+	      FIELD_PREP(MT_TXD7_SUB_TYPE, fc_stype) |
+	      FIELD_PREP(MT_TXD7_SPE_IDX, 0x18);
+	txwi[7] = cpu_to_le32(val);
+	if (!is_mmio) {
+		val = FIELD_PREP(MT_TXD8_L_TYPE, fc_type) |
+		      FIELD_PREP(MT_TXD8_L_SUB_TYPE, fc_stype);
+		txwi[8] = cpu_to_le32(val);
+	}
 
 	return 0;
 }