dmaengine: mcf-edma: Use struct_size()

Use struct_size() instead of hand writing it.
This is less verbose and more informative.

'mcf_chan' is now unused and can be removed. In fact, it is shadowed by
another variable in the 'for' loop below. Keep this one.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/97c2bb1c9b69d0739da3762a7752ae6582c4ad02.1683390112.git.christophe.jaillet@wanadoo.fr


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