constify ksys_mount() string arguments

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 2db2f4c..e272c24 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3295,8 +3295,8 @@ struct dentry *mount_subtree(struct vfsmount *m, const char *name)
 }
 EXPORT_SYMBOL(mount_subtree);
 
-int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,
-	       unsigned long flags, void __user *data)
+int ksys_mount(const char __user *dev_name, const char __user *dir_name,
+	       const char __user *type, unsigned long flags, void __user *data)
 {
 	int ret;
 	char *kernel_type;