arm64/mpam: fix a possible deadlock in mpam_enable

openEuler inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I3D58V


CVE: NA

----------------------------------

No unlock operation is performed on the mpam_devices_lock
before the return statement, which may lead to a deadlock.

Signed-off-by: Zhang Ming <154842638@qq.com>
Reported-by: Cheng Jian <cj.chengjian@huawei.com>
Suggested-by: Cheng Jian <cj.chengjian@huawei.com>
Reviewed-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>