md: factor out a helper exceed_read_errors() to check read_errors

mainline inclusion
from mainline-next-20231220
commit 1979dbbe328ca4e1d0f061c94381cfa03388088d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T02O

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1979dbbe328ca4e1d0f061c94381cfa03388088d



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Move check_decay_read_errors() to raid1-10.c and factor out a helper
exceed_read_errors() to check if read_errors exceeds the limit, so that
raid1 can also use it. There are no functional changes.

Signed-off-by: Li Nan <linan122@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231215023852.3478228-2-linan666@huaweicloud.com