mtd: plat-ram: add const quilifiers

Be a bit stricter and add few more 'const' qualifiers.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/include/linux/mtd/plat-ram.h b/include/linux/mtd/plat-ram.h
index e07890a..44212d6 100644
--- a/include/linux/mtd/plat-ram.h
+++ b/include/linux/mtd/plat-ram.h
@@ -20,8 +20,8 @@
 
 struct platdata_mtd_ram {
 	const char		*mapname;
-	const char		**map_probes;
-	const char		**probes;
+	const char * const      *map_probes;
+	const char * const      *probes;
 	struct mtd_partition	*partitions;
 	int			 nr_partitions;
 	int			 bankwidth;