std_serial_dev_acquisition_stop(): Remove dev_close_fn parameter

std_serial_dev_acquisition_stop(): Remove dev_close_fn parameter

All callers of std_serial_dev_acquisition_stop() currently pass the same
callback for the dev_close_fn parameter as the dev_close callback of their
sr_dev_driver struct. Remove the dev_close_fn parameter and invoke the
drivers dev_close() callback directly. This simplifies the API and ensures
consistent behaviour between different drivers.

Signed-off-by: Lars-Peter Clausen <redacted>