ar71xx: fix RB941-2nD detection

Some hAP lite routers aren't detected because
/proc/cpuinfo shows "RouterBOARD RB941-2nD"
instead of "RouterBOARD 941-2nD".

Fix that.
Signed-off-by: Julien Rabier <taziden@flexiden.org>
[Alter string to include all flavours + slight rewrite of commit msg]
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

target/linux/ar71xx/base-files/lib/ar71xx.sh

@@ -1092,7 +1092,7 @@ ar71xx_board_detect() {
 	*"RouterBOARD 931-2nD")
 		name="rb-931-2nd"
 		;;
-	*"RouterBOARD 941-2nD")
+	*"RouterBOARD"*"941-2nD")
 		name="rb-941-2nd"
 		;;
 	*"RouterBOARD 951G-2HnD")