mt76: mt7663s: fix rx buffer refcounting

Similar to mt7601u driver, fix erroneous rx page refcounting

Fixes: a66cbdd6

 ("mt76: mt7615: introduce mt7663s support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/dca19c9d445156201bc41f7cbb6e894bbc9a678c.1610644945.git.lorenzo@kernel.org