cfg80211: fix documentation format

Kernel-doc complains if the line isn't prefixed with an
asterisk, fix that.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20200320144110.2786ad5fb234.I369d103d11c71e39e3a3f97ed68a528c5b875f1e@changeid


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