thermal: core: Fix TZ_GET_TRIP NULL pointer dereference

Do not call get_trip_hyst() from thermal_genl_cmd_tz_get_trip() if
the thermal zone does not define one.

Fixes: 1ce50e7d ("thermal: core: genetlink support for events/cmd/sampling")
Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_netlink.c

@@ -419,10 +419,11 @@ static int thermal_genl_cmd_tz_get_trip(struct param *p)
 	for (i = 0; i < tz->trips; i++) {
 
 		enum thermal_trip_type type;
-		int temp, hyst;
+		int temp, hyst = 0;
 
 		tz->ops->get_trip_type(tz, i, &type);
 		tz->ops->get_trip_temp(tz, i, &temp);
+		if (tz->ops->get_trip_hyst)
 			tz->ops->get_trip_hyst(tz, i, &hyst);
 
 		if (nla_put_u32(msg, THERMAL_GENL_ATTR_TZ_TRIP_ID, i) ||