drivers: sensor: vcnl4040: fix I2C write function

The driver was using the i2c_transfer_dt() API incorrectly by not using the
I2C_MSG_STOP flag in the flags field.

The I2C write function can be written more simply with the basic I2C write
API so this commit also switches the code to the basic I2C write API to fix
this bug.

Signed-off-by: Nick Ward <nick.ward@ftpsolutions.com.au>