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>
diff --git a/drivers/spi/spi-uclass.c b/drivers/spi/spi-uclass.c
index a392a93..ba325cf 100644
--- a/drivers/spi/spi-uclass.c
+++ b/drivers/spi/spi-uclass.c
@@ -160,7 +160,7 @@
 {
 	struct dm_spi_slave_plat *plat = dev_get_parent_plat(dev);
 
-	if (!dev_of_valid(dev))
+	if (!dev_has_ofnode(dev))
 		return 0;
 
 	return spi_slave_of_to_plat(dev, plat);