HID: make ishtp_cl_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the ishtp_cl_bus_type variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/intel-ish-hid/ishtp/bus.c

@@ -378,7 +378,7 @@ static const struct dev_pm_ops ishtp_cl_bus_dev_pm_ops = {
 	.restore = ishtp_cl_device_resume,
 };
 
-static struct bus_type ishtp_cl_bus_type = {
+static const struct bus_type ishtp_cl_bus_type = {
 	.name		= "ishtp",
 	.dev_groups	= ishtp_cl_dev_groups,
 	.probe		= ishtp_cl_device_probe,