greybus: loopback: allocate a response even for a 0-byte request

If payload length of a transfer packet is 0, no response is allocated.
Send a well-formed response even in that case.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -533,7 +533,6 @@ static int gb_loopback_request_recv(u8 type, struct gb_operation *operation)
 			return -EINVAL;
 		}
 
-		if (len) {
 		if (!gb_operation_response_alloc(operation,
 				len + sizeof(*response), GFP_KERNEL)) {
 			dev_err(dev, "error allocating response\n");
@@ -541,8 +540,9 @@ static int gb_loopback_request_recv(u8 type, struct gb_operation *operation)
 		}
 		response = operation->response->payload;
 		response->len = cpu_to_le32(len);
+		if (len)
 			memcpy(response->data, request->data, len);
-		}
+
 		return 0;
 	default:
 		dev_err(dev, "unsupported request: %hhu\n", type);