msm: msm_bus: Add mutex to protect node_list

Static variable node_list list need to be protected with a mutex
to prevent race conditions and use after free cases.

Change-Id: I4790b06712b8a8b401f43418cfcc53b415fb0019
Signed-off-by: David Dai <daidavid1@codeaurora.org>
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>