thermal: fix ptr_ret.cocci warnings

drivers/thermal/tango_thermal.c:86:1-3: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

CC: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>