Update call out algorithm for iio hwmon instance
Update call out algorithm for iio hwmon instance

When readSysfsWithCallout() or writeSysfsWithCallout() get run, use the
instancePath to search for a call out path. For instances with an hwmon
driver, the passed in path should be used. For instances with an iio
driver, search for a phandle file that has a value matching to that in
the io-channels file for this phosphor-hwmon instance. If an error occurs
on the read or write, use that matching phandle path to create a call
out path.

Resolves openbmc/openbmc#1265

Change-Id: I6390d0dfb3d67ce8a55d171ca9a3cb8f3057a8c9
Signed-off-by: Brandon Wyman <cf665b64422a2d3418f6cc98ac9ad3a6d7fe7d95@us.ibm.com>

openbmc/phosphor-hwmon,openbmc/phosphor-hwmon