arm64/mpam: fix a possible deadlock in mpam_enable

hulk inclusion
category: bugfix
bugzilla: 51497
CVE: NA
Reference: https://gitee.com/openeuler/kernel/issues/I3D58V



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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(a)qq.com>
Reported-by: Jian Cheng <cj.chengjian(a)huawei.com>
Suggested-by: Jian Cheng <cj.chengjian(a)huawei.com>
Reviewed-by: Wang ShaoBo<bobo.shaobowang(a)huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi(a)huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>