usb: gadget: storage: fix sparse warning

fsg_common_set_inquiry_string() expects pointers
as second and third argument. Let's fix that by
passing NULL instead of plain 0 just so we silence
sparse's:

drivers/usb/gadget/f_mass_storage.c:3114:60: warning: \
	Using plain integer as NULL pointer
drivers/usb/gadget/f_mass_storage.c:3114:63: warning: \
	Using plain integer as NULL pointer
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/f_mass_storage.c

@@ -3111,7 +3111,7 @@ static int fsg_bind(struct usb_configuration *c, struct usb_function *f)
 					  fsg->common->can_stall);
 		if (ret)
 			return ret;
-		fsg_common_set_inquiry_string(fsg->common, 0, 0);
+		fsg_common_set_inquiry_string(fsg->common, NULL, NULL);
 		ret = fsg_common_run_thread(fsg->common);
 		if (ret)
 			return ret;