board: gateworks: gw_ventana: fix building with GCC 12.2

Building with GCC 12.2 results in an error

    board/gateworks/gw_ventana/gw_ventana.c:636:68: error: the comparison
    will always evaluate as 'true' for the address of 'pwm_padmux' will
    never be NULL [-Werror=address]
      636 |                 } else if (hwconfig_subarg_cmp(arg, "mode", "pwm") &&
          |                                                                    ^~

Remove the superfluous check.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-By: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>