mm: sharepool: Fix static check warning

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I612UG


CVE: NA

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Fix the following static check warning.
Use parentheses to specify the sequence of expressions, instead of using
the default priority.Should use parenthesis while use bitwise operator.

Fix this by add bracket in the expression.

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>