mac80211: fix channel assumption for association done work

Be consistent and use the wk->chan instead of the
local->hw.conf.channel for the association done work.
This prevents any possible races against channel changes
while we run this work.

In the case that the race did happen we would be initializing
the bit rates for the new AP under the assumption of a wrong
channel and in the worst case, wrong band. This could lead
to trying to assuming we could use CCK frames on 5 GHz, for
example.

This patch has a fix for kernels >= v2.6.34

Cc: stable@kernel.org
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>