wifi: nl80211: relax wdev mutex check in wdev_chandef()

In many cases we might get here from driver code that's
not really set up to care about the locking, and for the
non-MLO cases we really don't care so much about it. So
relax the checking here for now, perhaps we should even
remove it completely since we might not really care if
we point to an invalid link's chandef and can require
the caller to check the link validity first.

Fixes: 7b0a0e3c ("wifi: cfg80211: do some rework towards MLO link APIs")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>