samples, tests: Switch main return type from void to int

This applies the coccinelle script to another set of files:

   samples/bluetooth/bthome_sensor_template/src/main.c
   samples/boards/stm32/power_mgmt/standby_shutdown/src/main.c
   samples/drivers/smbus/src/main.c
   samples/drivers/virtualization/ivshmem/doorbell/src/ivshmem.c
   samples/fuel_gauge/max17048/src/main.c
   samples/hello_world/src/main.c
   samples/sensor/proximity_polling/src/main.c
   samples/subsys/logging/ble_backend/src/main.c
   tests/drivers/build_all/mfd/src/main.c

Signed-off-by: Keith Packard <keithp@keithp.com>