crypt: refix rd_LUKS_UUID handling

https://bugzilla.redhat.com/show_bug.cgi?id=533177

modules.d/50plymouth/cryptroot-ask.sh

@@ -17,7 +17,8 @@ if [ -n "$LUKS" ]; then
     ask=0
     luuid=${2##luks-}
     for luks in $LUKS; do
-	if [ "${luuid##$luks}" != "$2" ]; then
+	luks=${luks##luks-}
+	if [ "${luuid##$luks}" != "$luuid" ]; then
 	    ask=1
 	fi
     done

modules.d/90crypt/cryptroot-ask.sh

@@ -17,7 +17,8 @@ if [ -n "$LUKS" ]; then
     ask=0
     luuid=${2##luks-}
     for luks in $LUKS; do
-	if [ "${luuid##$luks}" != "$2" ]; then
+        luks=${luks##luks-}
+	if [ "${luuid##$luks}" != "$luuid" ]; then
 	    ask=1
 	fi
     done