qtnfmac: drop error reports for out-of-bounds key indexes

On disconnect wireless core attempts to remove all the supported keys.
Following cfg80211_ops conventions, firmware returns -ENOENT code
for the out-of-bound key indexes. This is a normal behavior,
so no need to report errors for this case.

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