Btrfs: fix crash of btrfs_release_extent_buffer_page

This is actually inspired by Filipe's patch.  When write_one_eb() fails on
submit_extent_page(), it'll give up writing this eb and mark it with
EXTENT_BUFFER_IOERR.  So if it's not the last page that encounter the failure,
there are some left pages which remain DIRTY, and if a later COW on this eb
happens, ie. eb is COWed and freed, it'd run into BUG_ON in
btrfs_release_extent_buffer_page() for the DIRTY page, ie. BUG_ON(PageDirty(page));

This adds the missing clear_page_dirty_for_io() for the rest pages of eb.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/extent_io.c

@@ -3677,6 +3677,7 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
 	if (unlikely(ret)) {
 		for (; i < num_pages; i++) {
 			struct page *p = extent_buffer_page(eb, i);
+			clear_page_dirty_for_io(p);
 			unlock_page(p);
 		}
 	}