dm table: fix write same support

If device_not_write_same_capable() returns true then the iterate_devices
loop in dm_table_supports_write_same() should return false.

Reported-by: Bharata B Rao <bharata.rao@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v3.8+
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-table.c

@@ -1442,7 +1442,7 @@ static bool dm_table_supports_write_same(struct dm_table *t)
 			return false;
 
 		if (!ti->type->iterate_devices ||
-		    !ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
+		    ti->type->iterate_devices(ti, device_not_write_same_capable, NULL))
 			return false;
 	}