driver core: Correct parameter check for API device_for_each_child_reverse_from()

device_for_each_child_reverse_from() checks (!parent->p) for its
parameter @parent, and that is not consistent with other APIs of
its cluster as shown below:

device_for_each_child_reverse_from() // check (!parent->p)
device_for_each_child_reverse()      // check (!parent || !parent->p)
device_for_each_child()              // same above
device_find_child()                  // same above

Correct the API's parameter @parent check by (!parent || !parent->p).

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://lore.kernel.org/r/20250105-class_fix-v6-5-3a2f1768d4d4@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -4050,7 +4050,7 @@ int device_for_each_child_reverse_from(struct device *parent,
 	struct device *child;
 	int error = 0;
 
-	if (!parent->p)
+	if (!parent || !parent->p)
 		return 0;
 
 	klist_iter_init_node(&parent->p->klist_children, &i,