xfs: calculate correct offset in xfs_scrub_quota_item

It's only used for tracepoints so it's relatively harmless,
but the offset is calculated incorrectly in xfs_scrub_quota_item.

qi_dqperchunk is the nr. of dquots per "chunk" which we have
conveniently *cough* defined to always be 1 FSB.  Therefore
block_offset * qi_dqperchunk == first id in that chunk,
and so offset = id / qi_dqperchunk

id * dqperchunk is ... meaningless.

Fixes-coverity-id: 1423965
Fixes: c2fc338c ("xfs: scrub quota information")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/scrub/quota.c

@@ -107,7 +107,7 @@ xfs_scrub_quota_item(
 	unsigned long long		rcount;
 	xfs_ino_t			fs_icount;
 
-	offset = id * qi->qi_dqperchunk;
+	offset = id / qi->qi_dqperchunk;
 
 	/*
 	 * We fed $id and DQNEXT into the xfs_qm_dqget call, which means