slim_msm: Satellite channel should not be deallocated more than once

It is possible that satellite channel deallocation is requested more
than once. (e.g. if the satellite times out waiting for response from
previous removal, then it will request removal again during
channel deallocation from its side).
Make sure that does not result in deallocating the channel more than
once.

CRs-fixed: 395926
Change-Id: I002635849bcaa7309de1fbddf1127c456bca6f20
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>