mt76: mt7603: fix watchdog rescheduling in mt7603_set_channel

Convert MT7603_WATCHDOG_TIME in jiffies rescheduling watchdog delayed
work

Fixes: c8846e10 ("mt76: add driver for MT7603E and MT7628/7688")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>