mm/mmzone.c: make "migratetype_names" const char *

Those strings are immutable in fact.

Link: http://lkml.kernel.org/r/20181124090327.GA10877@avx2Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -65,7 +65,7 @@ enum migratetype {
 };
 
 /* In mm/page_alloc.c; keep in sync also with show_migration_types() there */
-extern char * const migratetype_names[MIGRATE_TYPES];
+extern const char * const migratetype_names[MIGRATE_TYPES];
 
 #ifdef CONFIG_CMA
 #  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)

mm/page_alloc.c

@@ -236,7 +236,7 @@ static char * const zone_names[MAX_NR_ZONES] = {
 #endif
 };
 
-char * const migratetype_names[MIGRATE_TYPES] = {
+const char * const migratetype_names[MIGRATE_TYPES] = {
 	"Unmovable",
 	"Movable",
 	"Reclaimable",