qemu: command: Fix property name for start address of a pc-dimm module
    
    Starting a qemu VM with a memory module that has the base address
    specified results in the following error:
    
     error: internal error: early end of file from monitor: possible problem:
     2015-03-26T03:45:52.338891Z qemu-kvm: -device pc-dimm,node=0,memdev=memdimm0,
     id=dimm0,slot=0,base=4294967296: Property '.base' not found
    
    The correct property name for the base address is 'addr'.
    
    Signed-off-by: Luyao Huang <lhuang@redhat.com>