Now reading the data from the target device of the replace operation is allowed,
so the mirror number that is greater than the stripes number of a chunk is valid,
we will tune it when we find there is no target device later. Fix it.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>