iio: accel: adxl367: unlock on error in adxl367_buffer_predisable()

This error path needs to call the mutex_unlock(&st->lock) before
returning.

Fixes: cbab791c ("iio: accel: add ADXL367 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Link: https://lore.kernel.org/r/20220224150228.GB6856@kili


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>