hw/arm/raspi4b: remove redundant check in raspi_add_memory_node

hw/arm/raspi4b: remove redundant check in raspi_add_memory_node

The if (acells == 0 || scells == 0) check is redundant in
raspi_add_memory_node, since it is already checked in the call
chain, arm_load_dtb. Also the return value of the function is
not checked/used so it's removed.

Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20250902200818.43305-1-osama.abdelkader@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>