mac80211: ensure we don't update tx power on a non-running sdata

We can't update the Tx power on the device unless it is
running.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=101521

.

Cc: stable@vger.kernel.org
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>