msm: ipc_logging: Update function stubs

If IPC Logging is not enabled, but is still used, then the stubs will be
multiply defined because they are not static inline.

Make the stubs static inline.

CR-fixed: 456106
Change-Id: Id39c8f27acb952228b40012726e6b761defd16fb
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>
Signed-off-by: Arun Kumar Neelakatam <aneela@codeaurora.org>