dmaengine: imx-sdma: Fix a possible memory leak in sdma_transfer_init

If the function sdma_load_context() fails, the sdma_desc will be
freed, but the allocated desc->bd is forgot to be freed.

We already met the sdma_load_context() failure case and the log as
below:
[ 450.699064] imx-sdma 30bd0000.dma-controller: Timeout waiting for CH0 ready
...

In this case, the desc->bd will not be freed without this change.

Signed-off-by: Hui Wang <hui.wang@canonical.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20221130090800.102035-1-hui.wang@canonical.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>