[POWERPC] Fix device_is_compatible() const warning

Fix a const'ification related warning with device_is_compatible()
and friends related to get_property() not properly having const
on it's input device node argument.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/prom.c

@@ -1014,7 +1014,7 @@ EXPORT_SYMBOL(find_all_nodes);
 /** Checks if the given "compat" string matches one of the strings in
  * the device's "compatible" property
  */
-int device_is_compatible(struct device_node *device, const char *compat)
+int device_is_compatible(const struct device_node *device, const char *compat)
 {
 	const char* cp;
 	int cplen, l;
@@ -1491,7 +1491,8 @@ static int __init prom_reconfig_setup(void)
 __initcall(prom_reconfig_setup);
 #endif
 
-struct property *of_find_property(struct device_node *np, const char *name,
+struct property *of_find_property(const struct device_node *np,
+				  const char *name,
 				  int *lenp)
 {
 	struct property *pp;
@@ -1512,7 +1513,8 @@ struct property *of_find_property(struct device_node *np, const char *name,
  * Find a property with a given name for a given node
  * and return the value.
  */
-const void *get_property(struct device_node *np, const char *name, int *lenp)
+const void *get_property(const struct device_node *np, const char *name,
+			 int *lenp)
 {
 	struct property *pp = of_find_property(np,name,lenp);
 	return pp ? pp->value : NULL;

include/asm-powerpc/prom.h

@@ -134,7 +134,7 @@ extern struct device_node *of_find_all_nodes(struct device_node *prev);
 extern struct device_node *of_get_parent(const struct device_node *node);
 extern struct device_node *of_get_next_child(const struct device_node *node,
 					     struct device_node *prev);
-extern struct property *of_find_property(struct device_node *np,
+extern struct property *of_find_property(const struct device_node *np,
 					 const char *name,
 					 int *lenp);
 extern struct device_node *of_node_get(struct device_node *node);
@@ -158,9 +158,11 @@ extern void of_detach_node(const struct device_node *);
 extern void finish_device_tree(void);
 extern void unflatten_device_tree(void);
 extern void early_init_devtree(void *);
-extern int device_is_compatible(struct device_node *device, const char *);
+extern int device_is_compatible(const struct device_node *device,
+				const char *);
 extern int machine_is_compatible(const char *compat);
-extern const void *get_property(struct device_node *node, const char *name,
+extern const void *get_property(const struct device_node *node,
+				const char *name,
 				int *lenp);
 extern void print_properties(struct device_node *node);
 extern int prom_n_addr_cells(struct device_node* np);