platform: msm: msm_bus: Exit module init if misc register fails

If the misc_register fails to register the char device then handle
this case gracefully and exit else there will be a bad dereference
during the later part of the module init.

Change-Id: I7587ae236fba5ed65d336772369d1bf91bbc425c
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>