dm: core: Use dev_has_ofnode() instead of dev_of_valid()

We have two functions which do the same thing. Standardise on
dev_has_ofnode() since there is no such thing as an 'invalid' ofnode in
normal operation: it is either null or missing.

Also move the functions into one place.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/core/device.c

@@ -485,7 +485,7 @@ int device_probe(struct udevice *dev)
 	}
 
 	/* Only handle devices that have a valid ofnode */
-	if (dev_of_valid(dev)) {
+	if (dev_has_ofnode(dev)) {
 		/*
 		 * Process 'assigned-{clocks/clock-parents/clock-rates}'
 		 * properties