dmaengine: idxd: use const struct bus_type *

In the functions unbind_store() and bind_store(), a struct bus_type *
should be a const one, as the driver core bus functions used by this
variable are expecting the pointer to be constant, and these functions
do not modify the pointer at all.

Cc: dmaengine@vger.kernel.org
Acked-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Fenghua Yu <fenghua.yu@intel.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20230313182918.1312597-32-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dma/idxd/compat.c

@@ -16,7 +16,7 @@ extern void device_driver_detach(struct device *dev);
 
 static ssize_t unbind_store(struct device_driver *drv, const char *buf, size_t count)
 {
-	struct bus_type *bus = drv->bus;
+	const struct bus_type *bus = drv->bus;
 	struct device *dev;
 	int rc = -ENODEV;
 
@@ -32,7 +32,7 @@ static DRIVER_ATTR_IGNORE_LOCKDEP(unbind, 0200, NULL, unbind_store);
 
 static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t count)
 {
-	struct bus_type *bus = drv->bus;
+	const struct bus_type *bus = drv->bus;
 	struct device *dev;
 	struct device_driver *alt_drv = NULL;
 	int rc = -ENODEV;