PCI: endpoint: Make pci_epf_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the pci_epf_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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-pci-v1-1-300267a1e99e@marliere.net
[mani: modified subject to reflect subsys prefix]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/pci/endpoint/pci-epf-core.c

@@ -17,7 +17,7 @@
 
 static DEFINE_MUTEX(pci_epf_mutex);
 
-static struct bus_type pci_epf_bus_type;
+static const struct bus_type pci_epf_bus_type;
 static const struct device_type pci_epf_type;
 
 /**
@@ -507,7 +507,7 @@ static void pci_epf_device_remove(struct device *dev)
 	epf->driver = NULL;
 }
 
-static struct bus_type pci_epf_bus_type = {
+static const struct bus_type pci_epf_bus_type = {
 	.name		= "pci-epf",
 	.match		= pci_epf_device_match,
 	.probe		= pci_epf_device_probe,