Previously we return RAMBlock.offset; now return the pointer to the
whole structure.

ram_block_add returns void now, error is completely passed with errp.
Reviewed-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-Id: <1456813104-25902-2-git-send-email-famz@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>