Grow: fix removal of line in wrong case

Commit 18d9bcfa33939cee345d4d7735bc6081bcc409c8
removed wrong line (in case RAID0->RAID4).
This patch corrects this mistake
(line should be removed in case RAID4->RAID4).

Signed-off-by: Pawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>