AFS: Fix afs_prepare_write()

afs_prepare_write() should not mark a page up to date if it only partially
fills it in, in expectation of the caller filling in the rest prior to calling
commit_write(). commit_write(), however, should mark the page up to date.

Signed-off-by: David Howells <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/afs/write.c

···
 			_leave(" = %d [prep]", ret);
 			return ret;
 		}
-		SetPageUptodate(page);
 	}
 
 try_again:
···
 		spin_unlock(&vnode->writeback_lock);
 	}
 
+	SetPageUptodate(page);
 	set_page_dirty(page);
-
 	if (PageDirty(page))
 		_debug("dirtied");