hw/arm/sysbus-fdt: remove qemu_fdt_setprop returned value check

qemu_fdt_setprop asserts in case of error hence no need to check
the returned value.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
