wext: call cfg80211_set_encryption() with wiphy lock held

Similar to the previous commit, we need to hold the wiphy lock
here. There's a second instance that is correct already, fix
this one as well.

Fixes: a05829a7

 ("cfg80211: avoid holding the RTNL when calling the driver")
Link: https://lore.kernel.org/r/20210128183454.ea2f086465ed.I891d3bb44f068e6d97c160005010f052f28ab6e5@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>