ubi: Fix repeated words in comments

mainline inclusion
from mainline-v6.1-rc1
commit ec1f97f5
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9195H
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ec1f97f501a746403990515bbefcaecd7562b042



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Delete the redundant word 'a'.
Delete the redundant word 'the'.

Signed-off-by: Jilin Yuan <yuanjilin@cdjrlc.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>