usb: gadget: rndis: fix itnull.cocci warnings

The index variable of list_for_each_entry_safe is an offset from a list
pointer, and thus should not be NULL.

Generated by: scripts/coccinelle/iterators/itnull.cocci

CC: Geliang Tang <[e-mail]>
Signed-off-by: Fengguang Wu <[e-mail]>
Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/rndis.c

···
 	rndis_resp_t *r, *n;
 
 	list_for_each_entry_safe(r, n, &params->resp_queue, list) {
-		if (r && r->buf == buf) {
+		if (r->buf == buf) {
 			list_del(&r->list);
 			kfree(r);
 		}