dm table: pass correct dev area size to device_area_is_valid

Incorrect device area lengths are being passed to device_area_is_valid().

The regression appeared in 2.6.31-rc1 through commit
754c5fc7ebb417b23601a6222a6005cc2e7f2913.

With the dm-stripe target, the size of the target (ti->len) was used
instead of the stripe_width (ti->len/#stripes).  An example of a
consequent incorrect error message is:

  device-mapper: table: 254:0: sdb too small for target

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 42a3e43..9726577 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -1293,7 +1293,7 @@
 
 	for (i = 0; !ret && i < ms->nr_mirrors; i++)
 		ret = fn(ti, ms->mirror[i].dev,
-			 ms->mirror[i].offset, data);
+			 ms->mirror[i].offset, ti->len, data);
 
 	return ret;
 }