dmaengine: fsl-edma: remove redundant assignment to pointer last_sg

dmaengine: fsl-edma: remove redundant assignment to pointer last_sg

The pointer last_sg is being assigned a value at the start of a loop
however it is never read and is being re-assigned later on in both
brances of an if-statement. The assignment is redundant and can be
removed.

Cleans up clang scan-build warning:
drivers/dma/fsl-edma-common.c:563:3: warning: Value stored to 'last_sg'
is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220614184759.164379-1-colin.i.king@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>