Make the new simple_read_from_buffer() take a const src

buffer without complaints.

fs/libfs.c

@@ -441,7 +441,7 @@ void simple_release_fs(struct vfsmount **mount, int *count)
 }
 
 ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
-				void *from, size_t available)
+				const void *from, size_t available)
 {
 	loff_t pos = *ppos;
 	if (pos < 0)

include/linux/fs.h

@@ -1527,7 +1527,7 @@ extern int simple_fill_super(struct super_block *, int, struct tree_descr *);
 extern int simple_pin_fs(char *name, struct vfsmount **mount, int *count);
 extern void simple_release_fs(struct vfsmount **mount, int *count);
 
-extern ssize_t simple_read_from_buffer(void __user *, size_t, loff_t *, void *, size_t);
+extern ssize_t simple_read_from_buffer(void __user *, size_t, loff_t *, const void *, size_t);
 
 extern int inode_change_ok(struct inode *, struct iattr *);
 extern int __must_check inode_setattr(struct inode *, struct iattr *);