mm/shmem.c: constify anon_ops

Every other dentry_operations instance is const, and this one might as
well be.

Link: http://lkml.kernel.org/r/1473890528-7009-1-git-send-email-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

@@ -4078,7 +4078,7 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
 
 /* common code */
 
-static struct dentry_operations anon_ops = {
+static const struct dentry_operations anon_ops = {
 	.d_dname = simple_dname
 };