regulator: fixed: fix GPIO descriptor leak on register failure

In the commit referenced by the Fixes tag,
devm_gpiod_get_optional() was replaced by manual
GPIO management, relying on the regulator core to release the
GPIO descriptor. However, this approach does not account for the
error path: when regulator registration fails, the core never
takes over the GPIO, resulting in a resource leak.

Add gpiod_put() before returning on regulator registration failure.

Fixes: 5e6f3ae5c13b ("regulator: fixed: Let core handle GPIO descriptor")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Link: https://patch.msgid.link/20251028172828.625-1-vulab@iscas.ac.cn
Signed-off-by: Mark Brown <broonie@kernel.org>