fix(zynqmp): fix prepare_dtb() memory description

The commit 8ce2fbffe37d ("fix(zynqmp): fix BLXX memory limits for user
defined values") fixed logic around BL31_LIMIT but didn't update
prepare_dtb() which is also using +1 logic.

Change-Id: Ia6de10d992a552ca9cfa39c14261b0f94cda95ec
Signed-off-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Akshay Belsare <akshay.belsare@amd.com>
diff --git a/plat/xilinx/zynqmp/bl31_zynqmp_setup.c b/plat/xilinx/zynqmp/bl31_zynqmp_setup.c
index 2197b96..3598b53 100644
--- a/plat/xilinx/zynqmp/bl31_zynqmp_setup.c
+++ b/plat/xilinx/zynqmp/bl31_zynqmp_setup.c
@@ -212,7 +212,7 @@
 
 	/* Reserve memory used by Trusted Firmware. */
 	if (fdt_add_reserved_memory(dtb, "tf-a", BL31_BASE,
-				    BL31_LIMIT - BL31_BASE + 1)) {
+				   (size_t) (BL31_LIMIT - BL31_BASE))) {
 		WARN("Failed to add reserved memory nodes for BL31 to DT.\n");
 	}