qtnfmac: set valid edmg in cfg80211_chan_def

Make sure that edmg field of cfg80211_chan_def structure is properly
initialized by zeros. Otherwise cfg80211_chandef_valid may return
false if edmg fields contain some garbage.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>