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/timer/timer-uclass.c

@@ -54,7 +54,7 @@ static int timer_pre_probe(struct udevice *dev)
 	ulong ret;
 
 	/* It is possible that a timer device has a null ofnode */
-	if (!dev_of_valid(dev))
+	if (!dev_has_ofnode(dev))
 		return 0;
 
 	err = clk_get_by_index(dev, 0, &timer_clk);