staging: wfx: retrieve ampdu_density from sta->ht_cap

wvif->ht_info.ht_cap is a useless copy of sta->ht_cap. It makes no sense
to rely on it.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-12-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>