hostap: Fix outdated comment about dev->destructor

After commit cf124db5 ("net: Fix inconsistent teardown and
release of private netdev state."), setting
'dev->needs_free_netdev' ensures device data is released, and
'dev->destructor' is not used anymore.

Fixes: cf124db5 ("net: Fix inconsistent teardown and release of private netdev state.")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>