wifi: cfg80211: add missing kernel-doc for cqm_rssi_work

[ Upstream commit d1383077 ]

As reported by Stephen, I neglected to add the kernel-doc
for the new struct member. Fix that.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 37c20b2e ("wifi: cfg80211: fix cqm_config access race")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>