tools/iio/iio_utils:fix memory leak

1. fopen sysfs without fclose.
2. asprintf filename without free.
3. if asprintf return error,do not need to free the buffer.

Signed-off-by: Yulong Zhang <yulong.zhang@metoak.net>
Link: https://lore.kernel.org/r/20230117025147.69890-1-yulong.zhang@metoak.net


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