mac80211: Remove redundent assignment channel_type

Fix the following coccicheck warnings:

net/mac80211/util.c:3265:3: warning: Value stored to 'channel_type' is
never read [clang-analyzer-deadcode.DeadStores].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220113161557.129427-1-jiapeng.chong@linux.alibaba.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>