Bluetooth: SMP: Fix using HCI_ERROR_REMOTE_USER_TERM on timeout

This replaces the usage of HCI_ERROR_REMOTE_USER_TERM, which as the name
suggest is to indicate a regular disconnection initiated by an user,
with HCI_ERROR_AUTH_FAILURE to indicate the session has timeout thus any
pairing shall be considered as failed.

Fixes: 1e91c29e ("Bluetooth: Use hci_disconnect for immediate disconnection from SMP")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>