thermal/drivers/ti-soc-thermal: Use helper function IS_ERR_OR_NULL()

Use IS_ERR_OR_NULL() to detect an error pointer or a null pointer
open-coding to simplify the code.

Signed-off-by: Li Zetao <lizetao1@huawei.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230817014900.3094512-1-lizetao1@huawei.com