NET: mac80211: fix inappropriate memory freeing

Fix inappropriate memory freeing in case of requested rate_control_ops was
not found.  In this case the list head entity is going to be accidentally
wasted.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>