thermal: int340x: Prevent error in reading trip hysteresis attribute

Some of the INT340X devices may not have hysteresis defined in the ACPI
definition. In that case reading trip hysteresis results in error. This
spams logs of user space utilities.

In this case instead of returning error, just return hysteresis as 0,
which is correct as there is no hysteresis defined for the device.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>