iio: light: vcnl4000: update sampling periods for vcnl4200

Vishay has published a new version of "Designing the VCNL4200 Into an
Application" application note in October 2019. The new version specifies
that there is +-20% of part to part tolerance. This explains the drift
seen during experiments. The proximity pulse width is also changed from
32us to 30us. According to the support, the tolerance also applies to
ambient light.

So update the sampling periods. As the reading is blocking, current
users may notice slightly longer response time.

Fixes: be38866f ("iio: vcnl4000: add support for VCNL4200")
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Tomas Novotny <tomas@novotny.cz>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>