mt76: mt7615: fix max wtbl size for 7663

Current mt7663 offload firmware can support up to 32 wtbl entries

Fixes: f40ac0f3 ("mt76: mt7615: introduce mt7663e support")
Co-developed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>