gpio: of: initialize local variable passed to the .of_xlate() callback

of_flags is passed down to GPIO chip's xlate function, so ensure this one
is properly initialized as - if the xlate callback does nothing with it
- we may end up with various configuration errors like:

    gpio-720 (enable): multiple pull-up, pull-down or pull-disable enabled, invalid configuration

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Link: https://lore.kernel.org/r/20250708083829.658051-1-alexander.stein@ew.tq-group.com


[Bartosz: tweaked the commit message]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>