wifi: rt2x00: fix HT20/HT40 bandwidth switch on MT7620

Add missing configuration of the channel bandwidth filter to the
channel setup function for MT7620.

Reported-by: Serge Vasilugin <vasilugin@yandex.ru>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/1664d89ba149f7b0bcec18b2a2abaedf49654507.1663445157.git.daniel@makrotopia.org