thermal/drivers/mediatek/lvts: Fix debugfs unregister on failure

thermal/drivers/mediatek/lvts: Fix debugfs unregister on failure

When running the probe function for this driver, the function
lvts_debugfs_init() gets called in lvts_domain_init() which, in
turn, gets called in lvts_probe() before registering threaded
interrupt handlers.

Even though it's unlikely, the last call may fail and, if it does,
there's nothing removing the already created debugfs folder and
files.

In order to fix that, instead of calling the lvts debugfs cleanup
function upon failure, register a devm action that will take care
of calling that upon failure or driver removal.

Since devm was used, also delete the call to lvts_debugfs_exit()
in the lvts_remove() callback, as now that's done automatically.

Fixes: f5f633b18234 ("thermal/drivers/mediatek: Add the Low Voltage Thermal Sensor driver")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20250402083852.20624-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>