slim_ngd: Fix logical address notification mechanism

It's possible that multiple slaves report present and expect
corresponding notifications concurrently. Make sure notifications
are sent out in that case. Since notifications cannot be sent when
device doesn't have associated driver, make sure logical address
is not queried in that case.

Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>