core: make the chip file descriptor blocking

core: make the chip file descriptor blocking

After discussing this a while back we removed the call to fcntl() that
would make the request file descriptor non-blocking so that a call to
gpiod_line_request_read_edge_events() would block if no events are
pending. We agreed that the same behavior should apply to info events and
made the docs state that. Unfortunately we still pass the O_NONBLOCK flag
to open() making read() called on the chip file descriptor return
immediately if no info events are pending. Fix it by removing this flag.

Fixes: b7ba732e6a93 ("treewide: libgpiod v2 implementation")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>