wifi: rt2x00: correctly set BBP register 86 for MT7620

Instead of 0 set the correct value for BBP register 86 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/257267247ee4fa7ebc6a5d0c4948b3f8119c0d77.1663445157.git.daniel@makrotopia.org