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>

drivers/usb/gadget/config.c

@@ -50,7 +50,7 @@ usb_descriptor_fillbuf(void *buf, unsigned buflen,
 		return -EINVAL;
 
 	/* fill buffer from src[] until null descriptor ptr */
-	for (; 0 != *src; src++) {
+	for (; NULL != *src; src++) {
 		unsigned		len = (*src)->bLength;
 
 		if (len > buflen)