core: use gpiod_line_bulk_foreach_line_off()
core: use gpiod_line_bulk_foreach_line_off()

Use the newly introduced iterator macro wherever there's a need to
access the line offset while looping over a bulk object.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod