mac80211: fix register_hw error path

"cfg80211: fix alignment problem in scan request"
introduced a bug into the error path, because now
we allocate the entire scan request and not just
the channel list (the channel list is allocated
together with the scan request) -- on errors we
thus also need to free the entire scan request.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>