iio: light: tsl2563: use correct event code

The TSL2563 driver provides three iio channels, two of which are raw ADC
channels (channel 0 and channel 1) in the device and the remaining one
is calculated by the two.  The ADC channel 0 only supports programmable
interrupt with threshold settings and this driver supports the event but
the generated event code does not contain the corresponding iio channel
type.

This is going to change userspace ABI.  Hopefully fixing this to be
what it should always have been won't break any userspace code.

Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>