USB: "sparse" cleanups for usb gadgets

This removes complaints about the gadget stack which are generated by
the currrent "sparse":  it doesn't like the fact that zero is the null
pointer.  (Last I checked, C guarantees that's correct ...)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/gadget/m66592-udc.c b/drivers/usb/gadget/m66592-udc.c
index 700dda8..4b27d12 100644
--- a/drivers/usb/gadget/m66592-udc.c
+++ b/drivers/usb/gadget/m66592-udc.c
@@ -1299,7 +1299,7 @@
 	req->req.actual = 0;
 	req->req.status = -EINPROGRESS;
 
-	if (ep->desc == 0)	/* control */
+	if (ep->desc == NULL)	/* control */
 		start_ep0(ep, req);
 	else {
 		if (request && !ep->busy)