super1: fix sb->max_dev when adding a new disk in linear array

super1: fix sb->max_dev when adding a new disk in linear array

The value of sb->max_dev will always be increased by 1 when adding
a new disk in linear array. It causes an inconsistence between each
disk in the array and the "Array State" value of "mdadm --examine DISK"
is wrong. For example, when adding the first new disk into linear array
it will be:

Array State : RAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
('A' == active, '.' == missing, 'R' == replacing)

Adding the second disk into linear array it will be

Array State : .AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
('A' == active, '.' == missing, 'R' == replacing)

Signed-off-by: Lidong Zhong <lzhong@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>