arm64: zynqmp: Rename clocks as per the Arasan NAND driver

In zynqmp.dtsi file renamed "clk_sys" clock to "controller" and
"clk_flash" clock to "bus" as per upstreamed Arasan NAND driver.
This fixes NAND driver probe failure.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>