OF: add empty of_device_is_available for !OF

Add an empty version of of_device_is_available.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/include/linux/of.h b/include/linux/of.h
index a0f1292..95c8583 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -379,6 +379,11 @@
 	return 0;
 }
 
+static inline int of_device_is_available(const struct device_node *device)
+{
+	return 0;
+}
+
 static inline struct property *of_find_property(const struct device_node *np,
 						const char *name,
 						int *lenp)