If dma_get_slave_caps() fails, we need to release the dma channel before
returning an error to avoid leaking the channel.

Fixes: 2d6ca60f ("iio: Add a DMAengine framework based buffer")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20240723-iio-fix-dmaengine-free-on-error-v1-1-2c7cbc9b92ff@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>