mdadm/udev: Don't handle change event on raw devices

mdadm/udev: Don't handle change event on raw devices

The raw devices are ready when add event happpens and the raid
can be assembled. So there is no need to handle change events.
And it can cause some inconvenient problems.

For example, the OS is installed on md0(/root) and md1(/home).
md0 and md1 are created on partitions. When it wants to re-install
OS, anaconda can't clear the storage configure. It deletes one
partition and does some jobs. The change event happens. Now
the raid device is assembled again. It can't delete the other
partitions.

So in this patch, we don't handle change event on raw devices
anymore.

Signed-off-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Jes Sorensen <jes@trained-monkey.org>