minstrel: don't complain about feedback for unrequested rates

"It's not problematic if minstrel gets feedback for rates that it
doesn't have in its list, it should just ignore it. - Felix"

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Cc: Felix Fietkau <nbd@openwrt.org>
diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index f65ce6d..778c604 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -67,7 +67,6 @@
 	for (i = rix; i >= 0; i--)
 		if (mi->r[i].rix == rix)
 			break;
-	WARN_ON(i < 0);
 	return i;
 }