ubi: Reserve sufficient buffer length for the input mask

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8QZWQ


CVE: NA

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Because the mask received by the emulate_failures interface
is a 32-bit unsigned integer, ensure that there is sufficient
buffer length to receive and display this value.

Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>