Fix PHYMUX_5 register definition for mt7663 in
mt7615_mac_cca_stats_reset routine

Fixes: f40ac0f3 ("mt76: mt7615: introduce mt7663e support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>