s390/ap: make ap_bus_type const

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

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240203-bus_cleanup-s390-v1-5-ac891afc7282@marliere.netSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

drivers/s390/crypto/ap_bus.c

@@ -135,7 +135,7 @@ static int ap_max_domain_id = 15;
 /* Maximum adapter id, if not given via qci */
 static int ap_max_adapter_id = 63;
 
-static struct bus_type ap_bus_type;
+static const struct bus_type ap_bus_type;
 
 /* Adapter interrupt definitions */
 static void ap_interrupt_handler(struct airq_struct *airq,
@@ -1603,7 +1603,7 @@ static struct attribute *ap_bus_attrs[] = {
 };
 ATTRIBUTE_GROUPS(ap_bus);
 
-static struct bus_type ap_bus_type = {
+static const struct bus_type ap_bus_type = {
 	.name = "ap",
 	.bus_groups = ap_bus_groups,
 	.match = &ap_bus_match,