samples: peripheral_ht: drop device_get_binding()

Use DEVICE_DT_GET_ANY instead of hard-coding a device label property.
As far as I can tell from in-tree drivers, "TEMP_0" is nRF specific
and refers to nodes with compatible "nordic,nrf-temp", so use that and
clean up the driver Kconfig while we're here.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>