i2c: gpio_i2c_switch: fix gpio api misuse

Use GPIO_OUTPUT_INACTIVE to initialize the pin so that the ACTIVE_LOW DT
flag is honored and use the gpio_pin_set_dt functions to set the
(logical) value of the pin instead of gpio_pin_configure_dt, that
tries to reconfigure the pin each time.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>