thermal_genl_sampling_temp() misses to call nlmsg_free() in an error path.

Jump to out_free to fix it.

Fixes: 1ce50e7d ("thermal: core: genetlink support for events/cmd/sampling")
Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200929082652.59876-1-jingxiangfeng@huawei.com