staging: erofs: unzip_vle_lz4.c,utils.c: rectify BUG_ONs

commit b8e076a6ef253e763bfdb81e5c72bcc828b0fbeb upstream.

remove all redundant BUG_ONs, and turn the rest
useful usages to DBG_BUGONs.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>