imx21-hcd: use USB_DT_HUB

Fix  using the  bare number to set the 'bDescriptorType' field of the Hub
Descriptor while the value  is #define'd in <linux/usb/ch11.h>.
Signed-off-by: NSergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/imx21-hcd.c

@@ -1474,7 +1474,7 @@ static int get_hub_descriptor(struct usb_hcd *hcd,
 			      struct usb_hub_descriptor *desc)
 {
 	struct imx21 *imx21 = hcd_to_imx21(hcd);
-	desc->bDescriptorType = 0x29;	/* HUB descriptor */
+	desc->bDescriptorType = USB_DT_HUB; /* HUB descriptor */
 	desc->bHubContrCurrent = 0;
 
 	desc->bNbrPorts = readl(imx21->regs + USBH_ROOTHUBA)