xfs: fix again select in kconfig XFS_ONLINE_SCRUB_STATS

Commit 57c0f4a8 attempted to fix the select in the kconfig entry
XFS_ONLINE_SCRUB_STATS by selecting XFS_DEBUG, but the original
intention was to select DEBUG_FS, since the feature relies on debugfs to
export the related scrub statistics.

Fixes: 57c0f4a8

 ("xfs: fix select in config XFS_ONLINE_SCRUB_STATS")

Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>