In acpi_processor_add(), get_cpu_device() may return NULL in some cases
which is then passed to acpi_bind_one() and that will case a NULL
pointer dereference to occur.

Add a check to prevent that from happening.

[rjw: Changelog]
Signed-off-by: NHanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>