iio: light: vl6180: Drop unused linux/of.h include

Nothing from linux/of.h is used in this driver.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240218173323.1023703-2-jic23@kernel.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>