Add the missing unlock before return from function amd_pmc_send_cmd()
in the error handling case.

Fixes: 95e1b60f ("platform/x86: amd-pmc: Fix command completion code")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20210715074327.1966083-1-yangyingliang@huawei.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>