[readdir] constify ->actor

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index ac19c72..1402fcc 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -147,17 +147,16 @@
 {
 	int error;
 	struct fd arg = fdget(fd);
-	struct osf_dirent_callback buf;
+	struct osf_dirent_callback buf = {
+		.ctx.actor = osf_filldir,
+		.dirent = dirent,
+		.basep = basep,
+		.count = count
+	};
 
 	if (!arg.file)
 		return -EBADF;
 
-	buf.dirent = dirent;
-	buf.basep = basep;
-	buf.count = count;
-	buf.error = 0;
-	buf.ctx.actor = osf_filldir;
-
 	error = iterate_dir(arg.file, &buf.ctx);
 	if (error >= 0)
 		error = buf.error;