fs: constify tree_descr arrays passed to simple_fill_super()

simple_fill_super() is passed an array of tree_descr structures which
describe the files to create in the filesystem's root directory.  Since
these arrays are never modified intentionally, they should be 'const' so
that they are placed in .rodata and benefit from memory protection.
This patch updates the function signature and all users, and also
constifies tree_descr.name.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/libfs.c b/fs/libfs.c
index a8b62e5..a043953 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -507,7 +507,7 @@ EXPORT_SYMBOL(simple_write_end);
  * to pass it an appropriate max_reserved value to avoid collisions.
  */
 int simple_fill_super(struct super_block *s, unsigned long magic,
-		      struct tree_descr *files)
+		      const struct tree_descr *files)
 {
 	struct inode *inode;
 	struct dentry *root;