xfs: fix maxlevels comparisons in the btree staging code

mainline inclusion
from mainline-v5.15-rc4
commit 78e8ec83
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I76JSK
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=78e8ec83a404d63dcc86b251f42e4ee8aff27465



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The btree geometry computation function has an off-by-one error in that
it does not allow maximally tall btrees (nlevels == XFS_BTREE_MAXLEVELS).
This can result in repairs failing unnecessarily on very fragmented
filesystems.  Subsequent patches to remove MAXLEVELS usage in favor of
the per-btree type computations will make this a much more likely
occurrence.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
Signed-off-by: Long Li <leo.lilong@huawei.com>