slim_ngd: Fix logical address notification mechanism

It's possible that multiple slaves report present/absent and expect
corresponding notifications concurrently. Avoid using controller
resources where possible, and use list_for_each_safe to allow
changes to the device-list during list traversal.

Change-Id: I371c48d25a0953f5f1909c904e8fd80b599d16b3
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>