wifi: mac80211: do not pass a stopped vif to the driver in .get_txpower

Avoid potentially crashing in the driver because of uninitialized private data

Fixes: 5b3dc42b ("mac80211: add support for driver tx power reporting")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://patch.msgid.link/20241002095630.22431-1-nbd@nbd.name


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