MAINTAINERS: Update Zynq git tree location

The git tree for Zynq moved to Github. Update the MAINTAINERS record to
reflect the change.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

MAINTAINERS

@@ -1672,7 +1672,7 @@ M:	Michal Simek <michal.simek@xilinx.com>
 R:	Sören Brinkmann <soren.brinkmann@xilinx.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 W:	http://wiki.xilinx.com
-T:	git git://git.xilinx.com/linux-xlnx.git
+T:	git https://github.com/Xilinx/linux-xlnx.git
 S:	Supported
 F:	arch/arm/mach-zynq/
 F:	drivers/cpuidle/cpuidle-zynq.c