slim_msm: Do not deregister BAM if command-only pipes fail to init

Command only BAM pipes may fail to initialize post-SSR. We can still
use register-interface for sending commands to/from Slimbus.
In that case, do not deregister BAM handle since it is possible that
other BAM usecases (e.g. apps channels) will still need BAM.

Change-Id: I6c74394402c45933b4cde694e998c0d88e126114
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>