generic/204: sync before scrub hits EIO

Let's see if we can prevent fs corruption warnings by flushing dirty
data to disk before the test ends.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/204

@@ -18,6 +18,7 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _cleanup()
 {
 	rm -f $tmp.*
+	sync
 }
 
 # get standard environment, filters and checks