mt76: mt7615: Make mt7615_irq_handler static

Fix sparse warning:

drivers/net/wireless/mediatek/mt76/mt7615/pci.c:37:13:
 warning: symbol 'mt7615_irq_handler' was not declared. Should it be static?
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -34,7 +34,7 @@ void mt7615_rx_poll_complete(struct mt76_dev *mdev, enum mt76_rxq_id q)
 	mt7615_irq_enable(dev, MT_INT_RX_DONE(q));
 }
 
-irqreturn_t mt7615_irq_handler(int irq, void *dev_instance)
+static irqreturn_t mt7615_irq_handler(int irq, void *dev_instance)
 {
 	struct mt7615_dev *dev = dev_instance;
 	u32 intr;