[POWERPC] Make get_property() return a const void *

Previous changes have treated the return values of get_property as
const, so now we can make the actual change to get_property(). There
shouldn't be a need to cast the return values anymore.

We will now get compiler warnings when property values are assigned to
a non-const variable.

If properties need to be updated, there's still the of_find_property
function.

Built for cell_defconfig, chrp32_defconfig, g5_defconfig,
iseries_defconfig, maple_defconfig, pmac32_defconfig, ppc64_defconfig
and pseries_defconfig.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/prom.c

@@ -1527,7 +1527,7 @@ 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.
  */
-void *get_property(struct device_node *np, const char *name, int *lenp)
+const void *get_property(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

@@ -160,7 +160,7 @@ 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 machine_is_compatible(const char *compat);
-extern void *get_property(struct device_node *node, const char *name,
+extern const void *get_property(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);