ipmi: remve duplicate code in __ipmi_bmc_register()

__ipmi_bmc_register() jumps to the label 'out_free_my_dev_name' in an
error path. So we can remove duplicate code in the if (rv).

Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Message-Id: <20200720080838.148737-1-jingxiangfeng@huawei.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>