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: [e-mail]
Acked-by: Vinod Koul <[e-mail]>
Acked-by: Fenghua Yu <[e-mail]>
Acked-by: Dave Jiang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/dma/idxd/compat.c

···
 
 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;
 
···
 
 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;