mac80211_hwsim: fix number of channels in interface combinations

There's little point in setting the number of channels if the
entire combination struct is overwritten again later - that
was clearly intended the other way around, fix it.

Reported-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc drivers/net/wireless/mac80211_hwsim.c
Simple merge