minstrel_ht: move minstrel_mcs_groups declaration to header file

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Acked-by: Felix Fietkau <nbd@openwrt.org>
diff --git a/net/mac80211/rc80211_minstrel_ht.h b/net/mac80211/rc80211_minstrel_ht.h
index 696c0fc..462d2b2 100644
--- a/net/mac80211/rc80211_minstrel_ht.h
+++ b/net/mac80211/rc80211_minstrel_ht.h
@@ -29,6 +29,8 @@
 	unsigned int duration[MCS_GROUP_RATES];
 };
 
+extern const struct mcs_group minstrel_mcs_groups[];
+
 struct minstrel_rate_stats {
 	/* current / last sampling period attempts/success counters */
 	unsigned int attempts, last_attempts;