gpiolib: initialize return value in gpiochip_set_multiple()

gpiolib: initialize return value in gpiochip_set_multiple()

gpiochip_set_multiple() falls back to setting lines one by one when the
chip does not provide set_multiple(). If the fallback path receives an
empty mask, the loop is skipped and ret is returned without being
initialized.

Initialize ret to 0 so an empty mask is treated as a successful no-op.

Fixes: 9b407312755f ("gpiolib: rework the wrapper around gpio_chip::set_multiple()")
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://patch.msgid.link/20260620155319.79994-1-ruoyuw560@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>