board: siemens: iot2050: Fix mistake in list of writable env vars

This prevented to set m2_manual_config - as evaluated by
m2_connector_setup - under strict configurations for secure boot.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
1 file changed