ipmi_si: Fix wrong return value in try_smi_init()

On an error exit path, a negative error code should be returned
instead of a positive return value.

Fixes: 90b2d4f1 ("ipmi_si: Remove hacks for adding a dummy platform devices")
Cc: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Message-Id: <20201005145212.84435-1-tianjia.zhang@linux.alibaba.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>