mac80211: Properly set work-item channel-type.

Some were indirectly set to NO_HT (zero), but I think
it's better to explicitly set it in case the enum ever
changes.  In cfg.c, it seems the channel-type was just
ignored (and thus always set to NO_HT).

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>