ARM: zynq: DT: Update years in copyright

Trivial.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynq-7000.dtsi

@@ -2,7 +2,7 @@
  * Xilinx Zynq 7000 DTSI
  * Describes the hardware common to all Zynq 7000-based boards.
  *
- * Copyright (C) 2013 Xilinx, Inc.
+ *  Copyright (C) 2011 - 2015 Xilinx
  *
  * SPDX-License-Identifier:	GPL-2.0+
  */