binder: protect proc->threads with inner_lock

proc->threads will need to be accessed with higher
locks of other processes held so use proc->inner_lock
to protect it. proc->tmp_ref now needs to be protected
by proc->inner_lock.

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>