thermal/drivers/int340x/processor_thermal: Fix warning for return value

Fix smatch warnings:
drivers/thermal/intel/int340x_thermal/processor_thermal_device_pci.c:258 proc_thermal_pci_probe() warn: missing error code 'ret'

Use PTR_ERR to return failure of thermal_zone_device_register().

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210628183232.62877-1-srinivas.pandruvada@linux.intel.com