Disable 'duplicate front' switch for rear

The rear PCM needs to disable 'duplicate front' switch.

src/conf/cards/CS46xx.conf

@@ -21,9 +21,24 @@ CS46xx.pcm.rear.0 {
 	@args.CARD {
 		type string
 	}
-	type hw
-	card $CARD
-	device 1
+	type hooks
+	slave.pcm {
+		type hw
+		card $CARD
+		device 1
+	}
+	hooks.0 {
+		type ctl_elems
+		hook_args [
+			{
+				name "Duplicate Front"
+				lock true
+				preserve true
+				value 0
+				optional true
+			}
+		]
+	}
 }	
 
 <confdir:pcm/center_lfe.conf>