hw/arm/xlnx-zynqmp.c: Add missing error-propagation code

hw/arm/xlnx-zynqmp.c: Add missing error-propagation code

In some places in xlnx_zynqmp_realize() we were putting an
error into our local Error*, but forgetting to check for
failure and pass it back to the caller. Add the missing code.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20200324134947.15384-3-peter.maydell@linaro.org