iio: light: vcnl4000: update sampling periods for vcnl4040

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. Although the application
note is related to vcnl4200, according to support the vcnl4040's "ASIC
is quite similar to that one for the VCNL4200".

So update the sampling periods (and comment), including the correct
sampling period for proximity. Both sampling periods are lower. Users
relying on the blocking behaviour of reading will get proximity
measurements much earlier.

Fixes: 5a441aad ("iio: light: vcnl4000 add support for the VCNL4040 proximity and light sensor")
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Tested-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>