S70wr_date: bugfix in case no ntp file is there

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

userspace/rootfs_override/etc/init.d/S70wr_date

@@ -8,7 +8,7 @@ test -f $F || exit 0
 S=$(grep 'ntpserver' $F | sed 's/ntpserver//' | head -n 1)
 
 # if none, exit
-text -z "$D" && exit 0
+test -z "$S" && exit 0
 
 # pick busybox ntpd explicitly, to avoid real ntpd instances
 echo "Setting host time using ntpd"