Add parameter errp to memory_region_init_rom_device and update all call
sites to propagate the error.

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
[Propagate the error out of realize. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>