hwmon: (lm87) Allow channel data to be set from dts file

Currently there is no method for setting the channel
value from the DTS file. When, the driver uses a dts
file to initialize the driver platform_data is not set.
As a result channel variable may not be set correctly.

Without the channel variable set correctly, some of the
sensors will not be initialized correctly. For example
temp3 sensor sysfs entries.

This implements the schema agreed with the device tree
binding document.

Signed-off-by: Mahoda Ratnayaka <mahoda.ratnayaka@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>