wifi: iwlegacy: avoid fortify warning

There are two different alive messages, the "init" one is
bigger than the other one, so we have a fortify read warn
here. Avoid it by copying from the variable-sized 'raw'
instead.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230216203444.134310-1-johannes@sipsolutions.net