drm/panthor: avoid garbage value in panthor_ioctl_dev_query()

'priorities_info' is uninitialized, and the uninitialized value is copied
to user object when calling PANTHOR_UOBJ_SET(). Using memset to initialize
'priorities_info' to avoid this garbage value problem.

Fixes: f70000e ("drm/panthor: Add DEV_QUERY_GROUP_PRIORITIES_INFO dev query")
Signed-off-by: Su Hui <suhui@nfschina.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250119025828.1168419-1-suhui@nfschina.com

Author: Su Hui

drivers/gpu/drm/panthor/panthor_drv.c

@@ -802,6 +802,7 @@ static void panthor_query_group_priorities_info(struct drm_file *file,
 {
 	int prio;
 
+	memset(arg, 0, sizeof(*arg));
 	for (prio = PANTHOR_GROUP_PRIORITY_REALTIME; prio >= 0; prio--) {
 		if (!group_priority_permit(file, prio))
 			arg->allowed_mask |= BIT(prio);