wifi: mac80211: remove key data from get_key callback

This is now unused in nl80211, so there's no need to set
the pointer/length.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240627104411.f8ac49a8cfe0.Ic01f775903f0acd10b9ba77eb39d4ed50e709173@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>