iio:adc:berlin2-adc: Fix register definition

Active channel number is stored in BERLIN2_SM_CTRL as value, instead of a
bit map.
The masks for channel interrupts and data ready are a 16 bits wide bit
map each, instead of just 4 bits.

Also correct the data mask for the temperature sensor, which was
Reported-by: Antoine Tenart <antoine.tenart@free-electrons.com>

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Acked-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>