dmaengine: fsl-edma: use struct_size() helper

Make use of the struct_size() helper instead of an open-coded version,
in order to avoid any potential type mistakes or integer overflows that,
in the worst scenario, could lead to heap overflows.

Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Link: https://lore.kernel.org/r/20230821073600.4078584-1-liaoyu15@huawei.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>