usb: fix integer as NULL pointer warnings found by sparse

drivers/usb/host/ohci-sm501.c:93:24: warning: Using plain integer as NULL pointer
drivers/usb/gadget/amd5536udc.c:3254:9: warning: Using plain integer as NULL pointer
drivers/usb/gadget/amd5536udc.c:3267:9: warning: Using plain integer as NULL pointer
drivers/usb/gadget/amd5536udc.c:3277:9: warning: Using plain integer as NULL pointer
drivers/usb/gadget/amd5536udc.c:3285:9: warning: Using plain integer as NULL pointer
drivers/usb/gadget/amd5536udc.c:3293:9: warning: Using plain integer as NULL pointer

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/ohci-sm501.c b/drivers/usb/host/ohci-sm501.c
index 77204f0..e899a77 100644
--- a/drivers/usb/host/ohci-sm501.c
+++ b/drivers/usb/host/ohci-sm501.c
@@ -90,7 +90,7 @@
 	struct device *dev = &pdev->dev;
 	struct resource	*res, *mem;
 	int retval, irq;
-	struct usb_hcd *hcd = 0;
+	struct usb_hcd *hcd = NULL;
 
 	irq = retval = platform_get_irq(pdev, 0);
 	if (retval < 0)