dt: Add empty of_match_node() macro

Add an empty macro for of_match_node() that will save
some '#ifdef CONFIG_OF' for non-dt builds.

I have chosen to use a macro instead of a function to
be able to avoid defining the first parameter.
In fact, this "struct of_device_id *" first parameter
is usualy not defined as well on non-dt builds.
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of.h

@@ -303,6 +303,7 @@ static inline struct device_node *of_parse_phandle(struct device_node *np,
 }
 
 #define of_match_ptr(_ptr)	NULL
+#define of_match_node(_matches, _node)	NULL
 #endif /* CONFIG_OF */
 
 static inline int of_property_read_u32(const struct device_node *np,