xfs: fix scrub stats file permissions

When the kernel is in lockdown mode, debugfs will only show files that
are world-readable and cannot be written, mmaped, or used with ioctl.
That more or less describes the scrub stats file, except that the
permissions are wrong -- they should be 0444, not 0644.  You can't write
the stats file, so the 0200 makes no sense.

Meanwhile, the clear_stats file is only writable, but it got mode 0400
instead of 0200, which would make more sense.

Fix both files so that they make sense.

Fixes: d7a74cad ("xfs: track usage statistics of online fsck")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>