thermal/drivers/mediatek/lvts_thermal: Fix error check in lvts_debugfs_init()

thermal/drivers/mediatek/lvts_thermal: Fix error check in lvts_debugfs_init()

debugfs_create_dir() function returns an error value embedded in
the pointer (PTR_ERR). Evaluate the return value using IS_ERR
rather than checking for NULL.

Signed-off-by: Minjie Du <duminjie@vivo.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230921091057.3812-1-duminjie@vivo.com