cfg80211/mac80211: fix kernel-doc for SAR APIs

A stray @ caused the kernel-doc parser to not understand
this, fix that. Also add some missing kernel-doc.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 6bdb68ce ("nl80211: add common API to configure SAR power limitations")
Fixes: c534e093

 ("mac80211: add ieee80211_set_sar_specs")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au> # build only
Link: https://lore.kernel.org/r/20210106234740.96827c18f9bd.I8b9f0a9cbfe186931ef9640046f414371f216914@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>