platform/x86: ISST: Reset default callback on unregister

When multiple clients are registered and some of those modules are
removed, the default IOCTL callback for those clients are still not
NULL. Calling them will result in crash.

Set the default IOCTL callback pointer to NULL on unregister.

Signed-off-by: Srinivas Pandruvada <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>

Author: spandruvada

drivers/platform/x86/intel/speed_select_if/isst_if_common.c

@@ -831,6 +831,7 @@ void isst_if_cdev_unregister(int device_type)
 {
 	isst_misc_unreg();
 	mutex_lock(&punit_misc_dev_open_lock);
+	punit_callbacks[device_type].def_ioctl = NULL;
 	punit_callbacks[device_type].registered = 0;
 	if (device_type == ISST_IF_DEV_MBOX)
 		isst_delete_hash();