ARM64: zynqmp: clk: Add the clock for watchdog

The watchdog clock node is missing.
Add the same. This solves the below error.

cdns-wdt fd4d0000.watchdog: input clock not found
cdns-wdt: probe of fd4d0000.watchdog failed with error -2

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>