pwm: mediatek: Ensure to disable clocks in error path

pwm: mediatek: Ensure to disable clocks in error path

After enabling the clocks each error path must disable the clocks again.
One of them failed to do so. Unify the error paths to use goto to make it
harder for future changes to add a similar bug.

Fixes: 7ca59947b5fc ("pwm: mediatek: Prevent divide-by-zero in pwm_mediatek_config()")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250704172728.626815-2-u.kleine-koenig@baylibre.com
Cc: stable@vger.kernel.org
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>