[SCSI] correct attribute_container list usage

One of the changes in the attribute_container code in the scsi-misc tree
was to add a lock to protect the list of devices per container.  This,
unfortunately, leads to potential scheduling while atomic problems if
there's a sleep in the function called by a trigger.

The correct solution is to use the kernel klist infrastructure instead
which allows lockless traversal of a list.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>