cifs: convert list_for_each to entry variant in cifs_debug.c

convert list_for_each() to list_for_each_entry() where
applicable.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>