super1: make sure max_dev grows enough when adding a device to an array.

super1: make sure max_dev grows enough when adding a device to an array.

There was a few kernel releases where the kernel would shrink max_dev
to be just enough to hold the current number of devices.
More recent kernels never shrink it.
However to be as compatible as possible, if we notice that
max_dev is too small to successfully add a device, increase it.

Signed-off-by: NeilBrown <neilb@suse.de>