super1: Fix potential buffer overflows when copying cluster_name

super1: Fix potential buffer overflows when copying cluster_name

cmap_get_string() used to retrieve cluster_name does not restrict it's
size. To prevent buffer overflows use the size of the destination
buffer, not strlen() of the source, and null terminate the copied
string.

Fixes: 0aa2f15b ("mdadm: add the ability to change cluster name)"
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>