mt76: mt7615: fix MT7615_WATCHDOG_TIME definition

Express watchdog timeout in jiffies since it is used directly in
ieee80211_queue_delayed_work

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