slim_msm: ngd: Return success for channel removal during ADSP SSR

Slimbus master component resides on ADSP when this driver is used.
Wehn ADSP restarts, slimbus component goes down and bus is not
operational until it comes back up. During restart, slimbus clients
are notified since their device goes down, and the clients remove
channels and/or disconnect ports. Since bus is not operational,
return success for channel removal/port disconnection calls so that
the channel, port state is consistent with HW (not active, removed)

Change-Id: Ia2707ed9f3fc3573b5746c8e42fa7f229e0dea4f
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>