fs/buffer.c: remove duplicated assignment on b_private

bh->b_private is initialized within init_buffer(), thus the
assignment should be redundant. Remove it.
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/buffer.c

@@ -905,7 +905,6 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 
 		bh->b_state = 0;
 		atomic_set(&bh->b_count, 0);
-		bh->b_private = NULL;
 		bh->b_size = size;
 
 		/* Link the buffer to its page */