dt: eliminate OF_NO_DEEP_PROBE and test for NULL match table

There are no users of OF_NO_DEEP_PROBE, and of_match_node() now
gracefully handles being passed a NULL pointer, so the checks at the
top of of_platform_bus_probe can be dropped.

While at it, consolidate the root node pointer check to be easier to
read and tidy up related comments.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of_platform.h

@@ -52,9 +52,6 @@ extern struct platform_device *of_platform_device_create(struct device_node *np,
 						   const char *bus_id,
 						   struct device *parent);
 
-/* pseudo "matches" value to not do deep probe */
-#define OF_NO_DEEP_PROBE ((struct of_device_id *)-1)
-
 extern int of_platform_bus_probe(struct device_node *root,
 				 const struct of_device_id *matches,
 				 struct device *parent);