The pointer clean points the memory allocated by kmemdup, when the
return value of bch2_sb_clean_validate_late is not zero. The memory
pointed by clean is leaked. So we should free it in this case.

Fixes: a37ad1a3 ("bcachefs: sb-clean.c")
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>