crash_dump: don't log dm-crypt key bytes in read_key_from_user_keying

In the Linux kernel, the following vulnerability has been resolved: crash_dump: don't log dm-crypt key bytes in read_key_from_user_keying When debug logging is enabled, read_key_from_user_keying() logs the first 8 bytes of the key payload and partially exposes the dm-crypt key. Stop logging any key bytes.