arm64: zynqmp: rtc: Update rtc calibration value

As per the design specification
"The 16-bit Seconds Calibration Value represents the number of
 Oscillator Ticks that are required to measure the largest time
 period that is less than or equal to 1 second.
 For an oscillator that is 32.768 KHz, this value will be 0x7FFF."

Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynqmp.dtsi

@@ -691,7 +691,7 @@
 			interrupt-parent = <&gic>;
 			interrupts = <0 26 4>, <0 27 4>;
 			interrupt-names = "alarm", "sec";
-			calibration = <0x8000>;
+			calibration = <0x7FFF>;
 		};
 
 		sata: ahci@fd0c0000 {