msm: msm_bus_dbg: create dbgfs client handles

Now that clients are no longer crashing during probe
and/or unregistering with the bus driver as part
of their probe failure, let's add the client
dump files back to debugfs.

Change-Id: I100d79350e7395b0a388969984ebdc9e4f84b676
Signed-off-by: David Dai <daidavid1@codeaurora.org>