doc: fit: Write hex address as hex instead of int

When update_uboot.its is used directly there is syntax error for no reason.

Error report:
mkimage -f update_uboot.its boot
Error: update_uboot.its:18.12-13 syntax error
FATAL ERROR: Unable to parse input tree
mkimage: Can't read boot.tmp: Invalid argument

Fixes: 4bae90904b69 ("Automatic software update from TFTP server")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/doc/uImage.FIT/update_uboot.its b/doc/uImage.FIT/update_uboot.its
index c2ac266..aec4826 100644
--- a/doc/uImage.FIT/update_uboot.its
+++ b/doc/uImage.FIT/update_uboot.its
@@ -15,7 +15,7 @@
 			data = /incbin/("./u-boot.bin");
 			compression = "none";
 			type = "firmware";
-			load = <FFFC0000>;
+			load = <0xFFFC0000>;
 			hash-1 {
 				algo = "sha1";
 			};