wifi: mac80211: fix key lookup

With the split into keys[]/deflink.gtk[] arrays, WEP keys are
still installed into the keys[] array, but we didn't look them
up there. This meant they weren't deleted correctly.

Fix this by looking up the key there even if it's not pairwise
so we can be sure we don't have it.

Fixes: bfd8403a ("wifi: mac80211: reorg some iface data structs for MLD")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>