wifi: mac80211: properly skip link info driver update

If the interface isn't (yet) added to the driver, skip the
link info update. This was previously done for the BSS info
changes, but I forgot to copy the same check here.

Fixes: 7b7090b4 ("wifi: mac80211: split bss_info_changed method")
Reported-by:  <syzbot+bce2ca140cc00578ed07@syzkaller.appspotmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>