of: add empty of_find_node_by_path() for !OF

Add an empty version of of_find_node_by_path().
This fixes following build error for asoc tree:
sound/soc/fsl/fsl_ssi.c: In function 'fsl_ssi_probe':
sound/soc/fsl/fsl_ssi.c:1471:2: error: implicit declaration of function 'of_find_node_by_path' [-Werror=implicit-function-declaration]
  sprop = of_get_property(of_find_node_by_path("/"), "compatible", NULL);

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Rob Herring <robh@kernel.org>

include/linux/of.h

@@ -374,6 +374,11 @@ static inline struct device_node *of_find_matching_node_and_match(
 	return NULL;
 }
 
+static inline struct device_node *of_find_node_by_path(const char *path)
+{
+	return NULL;
+}
+
 static inline struct device_node *of_get_parent(const struct device_node *node)
 {
 	return NULL;