[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>
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 2a3d84a..bf2005b 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -1527,7 +1527,7 @@
  * 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;