slim: msm: Return success for ch-remove type of messages during SSR

During SSR, all channels are removed and ports are disconnected since
slimbus HW is not functional. Return success to clients for such
calls so that client can mark channel/port state constistent with HW

Change-Id: I9b18f8e7ffe233090c9612d0811a7d36645d0329
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>