tdx-cfg-block: fix off by one issue

Fix toradex_modules array off by one issue potentially leading to
spurious printout during boot e.g.

    Model: Toradex  V1.2A,

instead of

    Model: Toradex UNKNOWN MODULE V1.2A.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Acked-by: Max Krummenacher <max.krummenacher@toradex.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@toradex.com>