drivers:iio:accel:mma8452: added cleanup provision in case of failure.

mma8452_set_freefall_mode can return -ve value in case if
i2c_smbus_read_byte_data fails. This function is called from mma8452_probe,
and returning -ve value from probe indicates probe failure. Need to call
iio_triggered_buffer_cleanup & iio_trigger_cleanup in this case.

Signed-off-by: Bijosh Thykkoottathil <bijosh.t@hotmail.com>
Acked-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>