drivers: sensor: vcnl4040: fix sensor register init

The driver has a read register, modify value, write value flow due to
needing to modify nibbles of registers at different times.  The issue
this driver previously had was new incoming configurations from the
driver would be corrupted by previous configurations written into the
vcnl4040 (when there's been no power off). This would be in the case
when a device continuously power on and a developer is tweaking the
vcnl4040's configuration or when deploying firmware updates with
a new vcnl4040 configuration.

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